Sunset, you're doing really, really well under the terrible circumstances you find yourself.
Your WW has yet to feel the harsh light of reality, right now she's still in the mistaken mind-set that she's in control.
Even asking you to go to this family get together is crazy, it's all about her saving face, not dealing with the reality of the situation.
She has rejected you but still expects you to play nice and help her out, crazy making.
Stay the course Sunset, protect your self-respect, your self-esteem, because at your lowest point, that's what you've got, along with strength of character, honesty and morals.
You cannot be her protector and comforter any longer, she fired you from that job, but she has yet to realize the implications.
This has to be all about you now, your life, your future and your heart.
Your plans to part, sell and move away show your strength, that you won't tolerate this kind of treatment, and as she has no plans to give up the OM, the right thing to do for you.
As for contact with your WS, even though you are still in the same house (?) no chit chat, no comfort, treat this like a business wind-up, finances and dividing property only. If she's having a bad day, that's not your concern, in fact I would encourage you to fake it and act the opposite, like every day is a great day.
She may snap out of it, realize what she's giving up, but it's not likely, and in all honesty, unless she had been instantly completely remorseful, would you even want to try for R? It's very hard work, a lifetime of it.
Stay strong Sunset, we're all thinking of you and wishing you well.