Thank you for that. I was also continuing a relationship with his father for a time. That could have been argued to be my "choice."
But here's the thing, it's not. That kind of abuse beats a person down, it steals any sense of elf worth a person has. There's a headfuck where you hang onto the good that used to be, terrified to trade that for the unknown. For me, a lot of it was tied up in having a father in the home for my boys.
Add that all to being a man and the shame and stigma that comes with coming forward and saying your wife beats you.
I hope your bother-in-law finds his strength. Show him this story, He'll leave, but only when he's ready.