I normally stay away from the "college expense" threads, but... we, too, had a college expense clause included in our decree. Actually requested by Dad, for professional reasons. He made himself 100% responsible. Neither I nor my lawyer read carefully enough, as there was a loophole included - if either parent or relevant child did not agree with the college/university chosen, he didn't have to pay. Was I peeved when the time came? You betcha. But also held some grudging admiration for how well played that was. Both on the part of the ex and his attorney.
Could I have pushed it via court? Yep, and might have won. But at what cost? Legal fees eating up a good chunk of what I did have to contribute. Can't count on those being awarded. Luckily, both kids did well enough to end up tuition free, with just housing, etc. Both worked so as to contribute, both work-study and summers. And I think it made them value their education more.
Point being.... some hills are not worth dying on. Tell Mom and kids to suck it up and move along.
As for the cars? Why does a teen need a new car w/loans??? Sturdy beater. I "sold" my youngest (oldest never fancied driving) my 1997 standard trans Cherokee. No one else could drive it and I didn't have to worry (much) if she somehow rolled it. She drove that thing into the ground.
Just things to think about, OP.