@Ariadne - I know I don't poke my head in here too often, but I really have to second what kamap said. My wife and I have both dealt with similar situations from both our families (my parents, her grandparents - we no longer speak to either). The hardest part is truly understanding that it isn't your fault, there's nothing you can do to change them now, and there was never anything you could have done that would have changed the course of this. The frustrating part for me was that no matter how hard I tried to work things out and salvage relationships, it's completely impossible if one party will not admit any wrongs. I look at it this way; would I maintain contact with a friend who treated me this way? Would I feel bad about removing them from my life? That's a resounding no, for me. Family shouldn't get preferential treatment just because they happen to be related to you. Relationships are earned, not inherited.
If you haven't already, look into narcissistic parents and the psychology behind it. It really helped me to realize how their brains are working in these situations, and although I can't relate to it on a personal level, it helps to understand just why the hell they do some of the stuff that they do (and it always helps to see that there are many many people out there dealing with the same -or similar- situations). As kamap said, sometimes you just need someone to freaking LISTEN to you, so seeking out a professional (if that's an option) could be immensely helpful as well.
I'm terribly sorry you're having to deal with this. I wish you the absolute best, and hope that you can shed the guilt from this. You don't deserve it at all. Feel free to PM me anytime if you want to talk.