This is a painful thread for me, too.
I am estranged from my eldest sister (narcissistic to a horrifying degree, In addition to abusive to people who don’t validate her severely skewed world view).
I am also estranged from my youngest brother, another self-absorbed abuser.
My mother, who has been unhappy for as long as I can remember, is very close. Non-stop whining. And abuse when you don’t validate those whines. It’s draining. It feels like the energy is being sucked right out of me. I speak to the sibs I get along with and they tell me it’s the reason they don’t contact her very often, along with her never listening to a word we say, unless it’s to use those words as weapons against us. It affects my mental and emotional health badly.
Not long after my divorce, I moved in with my parents. Dad’s health was bad, and I wanted to help them if I could. I did. Unfortunately, Dad died last April. Since then, it’s been an almost non-stop litany from Mom about what a shit Dad was (He wasn’t. He had his faults, like all of us, and I loved him very much and miss him). I’m sick of it, literally. No amount of standing up to her, reasoning with her, or just plain saying, “You know, I’m not the person you should be telling this to. First, it’s all about 50 years in the past, and second, I’m his son. This is completely unfair.” Nope. She escalates. So it’s gotten to the point where I just get up and walk away from her, and talk to her seldom.
Good news is: a friend of mine has broached the subject of getting an apartment together. He’s kind and cheerful, which is usually my default as well…OK, I’m a little spacey too. I told him I’ll give it some serious thought. Well, if the offer’s still open, I’ll do it. We’re both rather poor. He’s going through a divorce right now, and mine wiped me out financially. If that doesn’t work, I’ll get my own apartment. If I can’t afford that, I’ll live in a van by the river! Seriously, almost anything would be better than living in a place that I look forward to getting away from…to my rather stressful job at a Customer Service desk at Home Depot. I like the job though. Meeting the challenges is very gratifying. They need to pay me more, though. 
Thanks for starting this thread, Plan B. It helps a lot to read what others have said, and to see that I need not feel bad about cutting off abusers. I feel no guilt about my brother and sister, but with Mom I guess I need to remind myself that “the well is poison” as QtM so aptly put it. I don’t want to see her bitter and alone at the end of her life, but she can make choices. Just like everyone else.