Back from the parents for Christmas. Just myself and my parents (I know!!), I only went because I didn't want to leave them on their own, even thought I'd much rather have spent it alone or with friends. My parents spent the weekend getting at each other, really nasty. Of course both think they are right and the other is completely unreasonable. My DM spoke to me a couple of times in no uncertain terms about being sick of DF, often speaks of a life without him. This has been going on my whole life. When we were teenagers I hoped she would just leave him, but he has changed and I love them both. But I really wish she would just grow a pair and do what she wants without dragging me into it. She seems to be waiting for me to do it for her, or tell her it's ok?? I'm not in this relationship, I'm not responsible but I think she feels that we are to blame because she has stayed with him for us - the children - like some kind of matyr (she loves to be a martyr)... ohh WIBU to pretend I'm working next year, stay in my PJs, turn off the phone and not see anyone??
Oh Xmas is a fabulous time for families to annoy and gripe at one another! Although from your thread it sounds like they've been doing it constantly. We all have our family crosses to bear over Xmas but if it is really that bad can you limit your time. You said for the weekend so I assume they live quite far away. Could you stay xmas eve (arriving at like 6pm), stay for brekkie and present opening and then leave at 10am to go to a friends for xmas lunch. Then you've seen them and celebrated without sending yourself totally around the bend!
But when she tells you about your df's failings, why don't you say what you said in your op? "Mum, do whatever you want - I'll support you in your decision - but please stop dragging me into it. I love you both, but your relationship is yours not mine." You don't even need to wai f Christmas to say it.
Perhaps your mother is afraid that if she does finally leave your dad you will pick sides and it won't be hers? You stated 'the children' so presumably you have siblings, have your discussed the situation with them?
I agree with Jux just tell your mum what you said in your opening post.
But also do not visit parents at Christmas if this is how you feel. Say you will spend Christmas doing something else, maybe helping a charity in a hospital or something.
You can tell them you will come the weekend before or after Christmas. That way if/when they do split up you won't get caught in a battle of who to spend Christmas with as you will have established already you are busy on Christmas day. And the only battle will be who gets you before Christmas or who gets you after Christmas!