This is an excellent question, and I'm so glad you asked! My best friend and I have been doing research on this very subject.

The Walsingham family charter was written to permit female heirs in the event that the man holding the title has no sons, and historically the family estate has been inherited by a woman before - that's why Alec is Lord Walsingham even though his surname is Underwood, because a Walsingham heiress married an Underwood centuries ago. So when Alec dies, Isabelle gets preference over the many male cousins who would take her place if she wasn't there. She is technically the heir.

However, you're right - Isabelle is not remotely prepared to inherit, and that's by design. Alec has sabotaged her social life, her education, her reputation, her confidence....She's completely without the tools needed to fill his shoes, and Alec has made no efforts to give her legitimate siblings. Alec has made plans for his criminal empire to be inherited by a young American upstart, Ridley (created by my friend Ira), but both his treatment of Isabelle and his plans with Ridley come from the same place: a complete repulsion from and refusal to cope with his own mortality. Alec refuses to accept that he's a mortal man who will one day die, and that the world will continue on without him and that plans should be made for a future where he doesn't exist. He'd just as soon have everything burn down when he goes.

So while technically Alec has plans for both the estate and his criminal empire once he's gone, they're only plans in the flimsiest sense, and are in a way designed to cause destruction once he - the keystone - is removed.

The first time, Isabelle didn't realize she was pregnant until the day of the abortion. Alec recognized the signs before she did, and brought her to parish vicar and former surgeon - yes, there's a whole story there - Clemency Holt to have the pregnancy terminated. To say Isabelle felt conflicted would be an understatement. She had a breakdown over whether she was supposed to be a good Christian or a good daughter and told Clemency what Alec had been doing to her, but he chose Alec's side, and Isabelle ended up accepting the abortion. I'd give more detail, but I plan on making this a fic, and I don't want to spell out everything. In the end she was left severely traumatized and spiritually damaged, and it's an incredibly painful page of her life she tries to never look back on.

As for the second time, Isabelle was also unaware that she was pregnant until the day of the miscarriage. It was very early in her pregnancy, and while she'd been feeling strange for some time, she didn't put two and two together until she started bleeding. She climbed into the bathtub and waited it out. At first she thought of this as this one a rare act of mercy on God's part, sparing her either having to get an abortion or bringing Alec's child into the world, but soon she was consumed with guilt over that and went once more to Clemency for spiritual guidance over how she should feel after losing her baby. The conversation they then had introduced to Isabelle the idea that the isolation she's locked in with Alec is actually harmful and unnecessary, paving the way for her relationship with Maggie Beth later on.

If Isabelle had stayed, eventually Alec probably would have impregnated her intentionally, but years down the road when she's more physically capable of bearing children. It would be incredibly taxing, especially psychologically. Good thing she got out!

While m!Isabelle has a less sympathetic view towards victims of sexual violence than canon Isabelle does, he's actually no more personally abusive. He still has a desire to be a good person, even if what that means to him is different than what it means to canon Isabelle, and while he shares Isabelle's history of abusing staff, he feels just as much guilt and repulsion about it as she does. He's more like his mother in other ways, primarily to do with ambition.

m!Viola and f!Alec still have a tightly knit, "hand in unlovable hand" type marriage. In some ways they're happier, because m!Isabelle's birth was much less traumatic and was consented to by everyone involved and because m!Viola is unaware that his spouse is fucking their child. However, m!Viola does feel somewhat emasculated by f!Alec, and can be prone to displays of anger or dominance to try to compensate.

Good eye! They would be the Cranes, actually, since f!Alec would've taken m!Viola's surname before Bertrand's death. f!Alec would've capitalized on what remained of the family name to bolster her own power, and restored them in the process.

m!Viola and m!Isabelle are both happier than in canon. Funny what having the iron fist of patriarchy softened will do for you! For m!Viola it's mostly the lack of childbirth trauma, and for m!Isabelle it's the less psychologically crippling nature of his parents' abuse. As for f!Alec, she pretends to think that feminism is all a bit above her mental pay grade, but really she sees her fellow women the same way she sees men: as prey. Thank you for all these excellent questions!

There are many reasons Alec doesn't go ahead and force Isabelle to carry his child the way he did Viola—and what happened to Viola is a large part of that. He would never risk Isabelle's life the way he did Viola's. Between the genetic risk for eclampsia and Isabelle's youth, an easy and safe pregnancy is unlikely. Then there's the problem of how to hide the pregnancy, and what to do with the baby if it's born...like you said, a risk to Alec's image.

However, Alec definitely wants to impregnate Isabelle—a way of deepening their bond, of laying claim to every aspect of her that he can—and plays it looser with contraception than he should. Isabelle has been pregnant by him twice, once at fifteen and once at nineteen or so, the former ending in abortion and the latter ending in miscarriage.

Hi!! Sorry this took so long to answer; I was gonna do a little sketch of the genderbent Underwoods to accompany my answer, but with holiday hours keeping my nose to the grindstone I've regrettably given up on that. Maybe some other time!

You're right that the Underwoods would all differ drastically in a genderbent AU! For simplicity's sake I'm going with cis genderbends, and assuming events still proceed more or less as they do in canon - that f!Alec still kills her mother and gets sent to Indonesia for it, for instance, and that things proceed the same with Morsden and Bertrand and everything. f!Alec would, I think, not be too different from canon Alec because of the way neither of them really buy into gender roles. Internally she'd be much the same. However, because of the way women are expected to behave in 19XX English high society, she'd present as much more gentle, humble, and self-effacing, and probably act primarily by steering the actions of her husband, m!Viola.

m!Viola would have more marked differences from canon than f!Alec. For one thing, he'd never have been a ballet dancer, and would have instead wanted to inherit the family business and restore the Crane family to its former glory. Being raised with that aim - not to mention being a manlet with a domineering, older wife who babytrapped him when he was eighteen - would see him with a chip on his shoulder, and he'd be more aggressive and likely to act out of anger/other emotions than Viola is canonically. Which leads me into some of the differences with m!Isabelle!

For clarity, m!Isabelle is still genderfluid, just AMAB instead of AFAB. One big difference would be that f!Alec would seek to raise him to be a proper heir. While she would still be psychologically, physically, and sexually abusive, she would keep this more under wraps, never crippling him and certainly never letting on to m!Viola that she's fucking their son - primarily because m!Viola would take this as being cuckolded by m!Isabelle, and would probably try to kill him. m!Isabelle would be raised with more freedom and better education, and would be encouraged into his parents' image rather than forced into the tiny pigeonhole that Isabelle gets in canon. As a result his compassionate tendencies would be more buried, and he'd be something of a tsundere about them, while also being in denial about the fact that f!Alec is abusing him at all. He'd like to think of it all as either consensual activity or just proper child-rearing. Nightmarish, I know.

If you have any specific questions about any of them, feel free to send them in! This is getting long.

Thank you very much for asking! As Alec groomed Isabelle for eventual abuse, he also groomed Viola to accept that abuse. It was very much a frog-in-a-pot thing. He knew that Viola's refusal to recognize that Alec groomed and abused Viola herself would keep her from seeing matters clearly, or indeed wanting to see them at all, so he purposefully groomed Isabelle right under her nose to build up Viola's repulsion - not to Alec, who she remained in love with, but to Isabelle. It was always going to be easier for Viola to reject the child she never really wanted than for her to reject the man she loved.

Viola went years "yes and"ing her own perception of what was happening between Alec and Isabelle. Nothing is wrong, but if something was, it would be because Isabelle is an attention whore. Nothing is happening, but if something was, it would be because Isabelle engineered it. She already hated Isabelle so it was easier for her to put the blame there for what she knew deep down was occurring but what she was able to deny until Isabelle, age fourteen and raped by Alec for the first time, came to her and told her what happened. Viola reacted with rage and accused Isabelle of seducing Alec deliberately and then lying about it in order to play the victim. It'll be a fic eventually, and I'll get to lay out Viola's emotional response - the way her own trauma is triggered, the way she goes on the offensive as a form of defense not only of her own psyche but her marriage and her way of life. It's a Lot.

After the fact, when Alec had returned from his business trip and life went on as usual but with this added awareness on Viola's part that Alec was fucking their daughter, Viola's hatred of Isabelle only deepened as her ability to ignore what was going on was put under further strain. So no, she wasn't pleased about it, but she chose again and again to blame Isabelle rather than risk jeopardizing what she actually cared about.

If we're talking total strangers who have only ever heard of him...Alec puts a lot of work into laundering his reputation. The first thing people tend to hear about him is his involvement in the Underwood Foundation, a non-profit organization dedicated to increasing access to medical care both domestically and internationally, in addition to war/disaster relief and refugee resettlement efforts. Alec's name, face, and grubby little mitts are all over the Foundation, so it's heavily associated with him and goes a long way towards making sure people think of him as close to sainthood.

More personally, Alec is known as a social butterfly, always hosting some social event or another. He and his wife are also known as patrons of the arts, having an impressive private art collection and devoting resources towards the preservation of art, and they're also both invested in a number of business endeavors independently - in Alec's case, particularly the shadow corporation now known as the Downgate Conglomerate, a controlling interest of which has been in the family for generations.

These are things that complete strangers with no connection to Alec might know from reading about him in the newspaper. If you want to know what people closer to him, but not close, think of him, that's a separate question. Thank you for asking!