I had to do the same as Marle....and I find my family relationships are SO much healthier now that I don't feel so trapped by all of the drama, inconsideration, gossip, complaints, and junk. And the distance I've put between us allows ME to control how much of that craziness I allow into my life.
What would be wrong with enforcing your boundaries as you state them? No, wait, hear me out here. If they feel glorious to even think about, isn't that telling you something? What would you lose by putting your foot down? Either they agree to abide by them (so you'll have greater peace of mind) or they don't (and you won't see much of them, so you'll have greater peace of mind)
Gaining dignity and respect doesn't have to be a fantasy.
Hugs,
GiveLove