How Can I Stop My Mother From Holding My 529 Hostage In Her Ongoing Divorce Against My Dad?

Location: Massachusetts. My (21F) parents have been engaged in divorce proceedings for the past two years. A year ago my mother threatened to use my college fund in lieu of her retirement if she was court ordered to pay money to my dad. It was in the back of my mind for a year but last week my dad informed me that she has given him a new proposal to finalize divorce proceedings. In this proposal he would be paying her alimony, plus 5000 dollars a month per child (me and my 18-year-old brother) in child support. Now I was under the impression my dad didn’t need to pay any child support because my brother and I are both legal adults but apparently this is not the case since we are both considered dependents of my mother. The part that scares me is she says she will pay for my grad school with MY 529 if my dad agrees to all this. If not, she will not pay for my grad school and would instead use my 529 to fund her own life. I legally cannot access the 529 as the beneficiary, I know that. She would have to pay a fine and taxes on any money she takes out. But she doesn’t care about that it seems. I have no idea how to stop her legally from using my 529 as a pawn. I’m currently applying to grad schools now and taking precautions like applying for financial aid, trying for a TA/GA position, looking in affordable places etc. I’m trying to avoid federal loans as much as possible but it seems like I’m being pushed into that corner more and more by my own mother. This isn’t fair to me or my dad, and I’m wondering if there is any legal way to stop her from doing this other than possibly suing (I do not wish to sue my own mother). I just feel failed by so many institutions right now because of this abuse of power and I need help.