I'd say to myself "Thank you for That".
Sounds sarcastic but it's not. I hated it when a trainer I had used to say it. But over the years I have come to realise what she was getting us to understand.
"Thank you for That" .... information about you, about your persistent behaviour, about your go to responses and so on.
Given that you have had this sort of behaviour from your SD before and you don't sound surprised by her actions - angry yes - disappointed by your OH, her dad, to intervene yes. And you already knew his "go to" position - little or no response.
You have and did have all the information you needed to reasonably predict his D's behaviour and it's effect on your Christmas expectations.
So maybe you need to ask yourself "What did I want the family Christmas to be, how did it look in your imagination" ?
Then ask yourself "How Likely was it - knowing what you already did about SD behaviour and OH GoTo response- for you to have a Christmas anything close to your Christmas Expectations?"
Then I think you have to accept that you knew before Christmas that you were never going to get the celebration anything close to what you wished for.
Also if I've read your post correctly your OH offered - wanted to go away- and you didn't. And it's OK that you wanted Your Christmas as you wanted it. But you were you ever going to get that Christmas?
His going away may be his way of "Getting Away From" his D behaviour and his dealing or not dealing with it. That's OK.
It's OK that you missed the cue - that you didn't see the clues - but now you are seeing them clearly. It's down to you what you do from here forwards.
Yes it is bad behaviour. Very bad behaviour, it's giving your SGC very bad messages, the AC is not being an Adult neither is she parenting. It's disrespectful, rude, it's abandoning of the younger child. It's wrong on so many levels.
However, it may be your SD and SGC's "Norms" and if they feel it's their "Parents Home" so even the AC reverts to being a teenager that is what they will do.
However much you didn't like your Christmas experience you can not change them. Your OH can not change them and it's not for you or him to try.
What you can do is ask yourself these questions :
What information did I already have about how they are likely to behave?
What was my Christmas Expectation?
Was I ever going to get anything close to my wish?
And the big one :
What do "I do" differently to make next year closer to how "I want" Christmas to be?
Going away will be an easy fix.
Firstly you won't be there to care for those "kids" of all ages - I'm including the SD the teenage SGD and your OH in the "Kids".
Also it may break the pattern of coming to yours so you can be the Parent/Grown Up and dogsbody to them.
Be angry, I'd be very angry but I would have to say I had enough information about How SD is that I should have taken different actions to look after myself and I didn't do that.
You wanted your OH to step in and be the Parent, the Grown Up and to either Stand Up With you or to Stand Up For You. Not an unreasonable wish but it seems as if the particular magic isn't going to happen for you. I'm sad for you about that.
But "Thank You For That" because now you are very clear about what you will get and what you won't get by way of your special Christmas.
You can not change another person unless they want to change so even if you OH had stood up with or for you it wouldn't have made much difference.
There probably would have been even more disruption/ Drama to upset you.
Do what You need to to take care of You and learn to use the information you have about other peoples behaviours honestly not to set yourself up for a hard time.
Good Luck and I am sad that you had to go through this Christmas for you to realise only those who care deeply for us care enough to work at changing their behaviour.
I hope you care enough about yourself to change your behaviour so you have better times.