Well, my mother is insane and thinks she shouldn't have to work. She never has, and the only reason she pays her bills is because people let her "borrow" money. She used to guilt trip me into giving her money, and I'm betting I've given her 10 grand over the years (while I was a college student working low-paying jobs, it's not like I was well-off!!). A few years back I said ENOUGH and stopped enabling her, and she guilt tripped me about that, too. She still calls me crying for money but I've just had to build a really strong backbone and not let the BS get to me. It's taken a lot of time for me to get to the point where I just block it out. And really, I communicate with her as little as possible, maybe once every other month. I have BEGGED the people I know give her money to stop because all it does is make my life more difficult because I have to hear how so and so helps her out but her own daughter refuses to help. If everyone would stop giving her money, she would have to work because she's not going to starve! And if she is that unwilling to help herself then that's HER problem! I'm terrified about what's going to happen when she gets old. She has no savings, no plan, nothing. Okay now my blood pressure is rising. But all of these people who enable her just assume I'll take her on, and that's not happening.
Anyway, I'm rambling, but here's what I've "figured out" about enablers - they aren't going to stop. These people know how my mother is, I'm sure your mother knows how your father really is, but that doesn't matter. I don't mean to be offensive, but I think enablers are really weak people. When I was enabling my mother it was because I didn't want to deal with her BS. It was easier for ME to just placate her than to stand up to her. I will say, when I finally put a stop to it, there was a huge blow up, she screamed and cried, accused me of being hateful, said it wasn't fair because my husband is rich (as in, we pay our bills), and on and on... maybe your mother just doesn't have the strength or desire to tell your dad the truth about his behavior. I really don't know what you can do or say to get her off your back without dealing with drama.
Personally, I would just tell her that you have cut ties with your father because his behavior is (insert the feeling it gives you here) and that's the situation. Tell her that he knows why your relationship is strained, and unless he changes his behavior, your relationship will not improve. Tell her it's hard enough for YOU to not have a relationship with your own father, so you don't need her trying to make you feel worse. Let her know that from now on you don't want to talk to her about him anymore, so if she wants to keep a relationship with you then she needs to respect you enough to knock it off. I'm going to warn you, she will likely freak out, so you really have to decide what is necessary for your sanity. What will be worse? Telling her that you can't deal with her behavior or dealing with her behavior?
Okay that was really long, but this is something I've dealt with for so long, it bugs the crap out of me to hear about other people dealing with it!