I am so sorry if you think anyone on this BB has insulted you. You are in a devilishly difficult situation, no doubt about it, and painful too. I can feel your pain coming out at me through the computer screen.
Just want to point out one thing before I go on, your kids are just that - kids. Of course they want you there for Christmas, don't expect them to be mature enough to understand your POV. They are not adults to understand your point of view in this yet. They just want their MUM.
But Andy is a big boy, and if can't see that having both you and OW or her daughter around at Christmas is not appropriate, then he has a lot of growing up to do.
Jo, I really hesitate to say this, because there are some here who will probably accuse me of seeing everyone's WAS as a narcissist (not so), but this is what Andy screams at me. He appears to be an absolutely self-centred person, who hasn't grown up at all, and has no idea of empathy. Arrogant, devious, says whatever works for him at that particular moment and then "can't remember" saying it later, a user, and on and on. He has you just where he wants you. Waiting on his every crumb. He loves controlling the situation. And you.
Have you looked up stuff about Narcissistic Personality Disorder? If not, here are some links -
The Web of Narcissism (members only, say where you heard about the site and mention Livnlearn if you want)