You need to wake up to the fact that you are dealing with someone who is NOT like you, and not playing by normal rules.
You have to shut down conversations, refuse to engage. be bald and outright about it if you need to.
No MIL, we don't need to talk about paint colours/dinner/the way the wind blows, we're happy with our choices and don't need to share them or get permission from anyone.
No, I appreciate you feel entitled to comment on our lives, but really, you really aren't.
My sister's dating is her business, I'm not going to discuss it with you.
We've been here before MIL, it ended badly, let's stick to you and your business shall we?
You need to talk to your DH. chances are he feels the same.
if he wants to limit his exposure to her, let him. likewise any DC you have. make sure that on every level possible, you need to fail to support any contact with her whatsoever.
stop hosting christmas. say that you are going to have a quiet one or a year off and that you have hosted enough and it's time to let someone else have a turn. mean it.