When I did try to talk to my DH in January about how upset I was at leaving my mum and sis on Christmas Day, it did not go well. The highlight of that talk was him saying he wished my mum was dead, like my dad, that way it wouldn't be an issue.
That's an awful thing to say, but why do you blame him so completely?
You seem to have a big grudge against your MIL; and your DH. He may be a complete tosser but from what you've said here, the person firmly in the wrong was your Mum. She turned up unannounced, knowing you'd have alternate plans, refused to go along with the plans and then tried to take you away from your planned Boxing Day activities.
Added to that, she only turns up as an 'add on' to business trips or visiting your sister, and your husband is probably sick of her saying Jump and you asking how high. She should have asked to come, and if it was late notice, been willing to go to MILs or engage with MILs at yours or whatever the plan was. She needed to think about YOUR family, not just hers.
Blaming DH for it seems an incredibly off-course decision. Why do you? Because his MIL is reliable? Because you'd rather see her less? Because you're a bit jealous that his MIL is there and your mum isn't?
I don't even think it's an issue of needing to stand up for yourself. It's just an issue with your mum, and it sounds like there have always been plenty of those. If you are angry, direct it solely at her.