About ten years ago after a particularly traumatic incident, I wrote my alcoholic mother and told her that if she ever called me again while drunk, I'd never speak to her again, and I meant it. Luckily, I wasn't forced to actually carry through, because she's never called me drunk since. However, I almost considered cutting her out of my life again a few years ago over some other stuff, but some relatives talked me down from it.
At this point, it's very sanity-saving for me to simply distance myself from her mentally and regard her as some distant and cordial aunt, rather than "mom."
If whatever is going on is something you feel is absolutely a deal-breaker for any sort of future relationship, I'd say your best bet is to confront them, perhaps in writing, and say, "I cannot tolerate this behavior and if it continues, we will no longer have a relationship."
Good luck.