Hello everyone

I'm new to the boards. With Christmas approaching I've decided to stop just reading and researching and actually participate a little.
My family dynamic is complicated. I've known for a while that my sister has BPD (un-diagnosed) and depression, and that my father is a long-term alcoholic - but recently I've been looking closer at my mother's behavior over the years and I'm beginning to think that she might have BPD too. Mum's a little more subtle than sis, I think that's why it took so long to see it for what it is.
Sis will scream and cry and rage about how awful we all are, how her problems are all our fault, how our family isn't normal - Maybe our family isn't normal but her perception of reality is skewed. It's that black and white demonizing, we never do anything right. She has endless demands and hoops to jump through but no amount of effort is good enough.
Mum though, is underhanded. She has what I've dubbed her "fake voice" that lets me know that the seemingly nice thing she's saying isn't true. I'll get comments like "Oh you're looking so slim today" with eye-roll or "That's a nice cleavage you're showing off" while giving me a disapproving look. It's always backed up with a snide little comment or a roll of the eyes. Mum cares very much about appearances, perfection.
She purposefully does things she knows will upset me. She used to go through my room, still goes through my bag / belongings. A couple of times she "cleaned" my fish tank and there were less fish left in there afterwards than before she cleaned it (the tank didn't need cleaning). If she finds anything important like documents, a copy of my birth certificate etc she throws it away. She opens my mail and pretends it was already open. She'll never admit to doing any of these things, she denies it or plays stupid like she can't remember what happened.
There's no privacy at all, she's got no concept of personal space. Mum will walk right into my room without knocking and then laugh at me if she catches me changing or doing something embarrassing. It makes me so uncomfortable and she knows it. I've always felt like I have to be ready for anything, constantly on guard. She breaks promises like they're nothing, I can't trust her word.
Since my sister cast me in the role of therapist many years ago, all of my effort over the years has gone toward figuring out some of her issues and also my own. Sis has lived interstate for about 2 years now, and I've gone LC for about the last year out of sheer emotional exhaustion. In that time I've finally managed to figure out my own problem (cPTSD). But now the more I think about mum the more I wonder why it's never occurred to me before.
We don't usually do much for Christmas but this year my Aunt and Cousin are coming from interstate so we're doing both Christmas Eve dinner with my Grandmother and then Christmas Day lunch as well. Sis says she's coming but we don't know for sure or when, she doesn't give us notice, she just shows up.
The problem I'm having is that while it's hard enough doing the usual Christmas stuff with my BPD sister, the extra people will be just as challenging. We very rarely see my Aunt, I really don't know her, but when we do see her she makes as much of a scene as my Sis does. My Aunt is an alcoholic like my father, and she's in the middle of a messy emotional divorce. She and my Grandmother clash and argue all the time (my GM can be very insensitive).
I just want to escape somewhere and not see anybody, and that makes me feel so guilty. I just know that it's all going to be one big disaster or a string of smaller disasters.
Thanks for letting me vent, sorry this ended up so lengthy. I've been keeping it all bottled up for a very long time. Reading everyone's stories on here has been so enlightening, knowing that others have gone through similar experiences.