I'm so sorry you have to deal with this!! I really don't have too much else to add to what everones else has said but wanted to let you know, you also have my hugs and support!
My biological father was a drunk, used drugs and was abusive to my mom. She left him when I was in the 6th grade. Luckily, I was young enough not to remember a whole lot of it. But now my mom is re-married and her husband isn't exactly a role model. He doesn't drink much but when he does he is very abusive. He is also very jealous. Once when I was 16, he and I got into a fight because of the way he was treating my mom and he actually swing at me. I told my mom that day that she had to choose between him or me and she choose him. It was very difficult. I didn't talk to my mom very much for a few years but now we talk all the time on the phone. I've learned that until she is ready to make a change, nothing I say will matter so I just don't even bring it up anymore. Now I just try to support her as best as I can and know there is nothing else I can do.
Would it do any good if you had your mom talk to a lawyer? Maybe if someone in "power" told her that she wouldn't loose the house or kids she might be more willing to do something? Its a tough situation no matter. Hang in there!
-------------------- Taking it one day at a time.....