Depends on when and how! If Viola tried to intervene after the overt abuse was already ongoing, there are two ways it could go: either she gets Isabelle out before Alec even knows what's happening (a la Nullverse) or he finds out what she's up to and kills her over it (a la my friend Ira's delectable fic A Family Portrait, which I will be linking below).

However, I've had plenty of AUs where Viola finds out while the abuse is still more covert - that is to say, while Isabelle is less than fourteen years old and Alec hasn't raped her yet. In those cases I think Viola might genuinely try to kill Alec, or else take Isabelle and run. Afterwards she'd try to be a better mother to Isabelle, but would still struggle to mend the gaping wound between them. As I always say, we live in the worst Viola timeline.

Oh, good, Halloween questions!

Isabelle loves to be spooked. Scary movies, haunted houses...He's a bit of a thrill seeker, and being scared in safe fun ways usually makes him jump and shriek, then laugh as he tries to catch his breath.

Meanwhile, Alec is very unsatisfying to scare. He's hard to scare in the first place, and even when you've successfully startled him, he's good at repressing his reactions except for maybe a jolt at most. However, he'll happily over-perform against his own nature to entertain people if he likes them enough.

Viola only really lets people she's very close to scare her for fun. Aster, Andre, and Alec (lord, I need to kick the A-name habit) are the only examples that come to mind. With anyone else she'd be very crabby if they tried it, but with those she loves, she'll laugh once she's recovered from the fright.

Ridley Villarreal (created by my dear friend @underground_ira on AO3) is one of Alec's favorite victims/lovers, who Alec eventually names as his heir in the criminal underworld and who he (albeit reluctantly) plans to marry Isabelle to as societal pressures to see her married off increase. Ridley and Alec met when Ridley was thirteen and Alec was thirty-eight. Ridley's stepfather was a business associate of Alec's in London, and Ridley was young and angry and full of hormones, all things Alec could exploit. As Ridley aged Alec inducted him into the underworld similarly to how Morsden had once done for Alec, and after Alec's eventual death, Ridley - backed by Viola - would come to inherit his position.

However, I would be remiss not to mention that Ridley is so much more than that. I love him and his place in my setting, but Ridley was created as I mentioned by my friend Ira and has a whole setting, surrounding characters, and canon unto himself - that the Underwoods also appear in in AU form! Ridley Wolfe, as he's called in that universe, is honest to God one of my favorite characters in anything ever. As a depiction of the cycle of abuse, of psychotic disorders, and of healing and finding fulfillment after abuse, he's absolutely riveting and has given me a lot of catharsis. I highly, highly recommend checking him out on AO3, and will link Ira's account below!