Relationships: Ultimatum from the In-Laws

I have been married for 19 years and have spent more than 15 of those years investing in my relationship with my in-laws (mother and father-in-law, brothers-in-law). I have drastically bent my values and myself to fit and meet their expectations and did it willingly to try and live at peace with them. By doing this, I wasn’t living at peace with myself. After finding LCS, I began to set firm boundaries. I expected my in-laws to throw a fit. I expected push-back and adult temper tantrums. During my last boundary issue with them concerning my brother-in-law asking us to pay for his children’s daycare for the summer, we declined and let them know that paying for them or their children is not something we will be doing in the future.

Boundary: IF YOU (ask us to pay for you or your children) I WILL (say no.)

This was a VERY hard boundary for my brother-in-law and his wife to accept. My in-laws have now taken an US or HER stance with my husband. Let US air all of our grievances with HER over the last couple years and make HER apologize or my husband, myself and our children are no longer welcome at holidays, etc…

I have A LOT of thoughts and feelings about how they shouldn’t be acting this way and making these types of crazy ultimatums and demands. What I want to do is accept their ultimatum and move on with my life, but when I take my husband’s feelings into consideration I’m thinking I’m trapped.

C: In-laws said, “Let US air all of our grievances with HER over the last couple years and you make HER apologize, or you and your kids are no longer welcome at holidays, etc…
T: I’m trapped between wanting to do what’s best for me and wanting to support my husband’s relationship with his family.
F: Trapped
A: Crying, arguing with husband, ruminating, getting friends’ opinions to gather evidence and support for what I want to do, buffering with food and Netflix, avoiding in-laws calls/texts, avoiding discussions with my husband, moping around the house, not fully engaged with work, catastrophizing, future tripping, judging my in-laws, judging myself, cognitive dissonance
R: Stay trapped

I do NOT want to camp out in the land of confusion. I’m not confused about what I want to do. I am troubled with how my husband will miss out on his family if I choose to do what I want to do. I know he will stand by my side, but I don’t want to put him in a position to choose one over the other.

How do I hold to my boundary and do what I want while being considerate of my husband and his relationship with his family?