She declared a vacation and now wants to trade it for something during the summer? I don't know whether she has legal ability to cancel her vacation notice and re-use her vacation time time for the summer, that's probably more a lawyer question. She ought to be welcome to cancel and you can agree to keep the kids while she is gone. After all, the more the kids are with you, the better for your husband and you, and especially the kids.
Missing a Disney trip isn't a disaster for the kids. (The disaster is her leaving the kids behind for her BF.) I was at DisneyWorld nearly 10 years ago, paid about $100 each for myself and son, and we rode only 6 rides all day. And 3 of them were in the park's last hour during the fireworks when the Magic Mountain roller coaster had no line. By contrast, less than an hour from home I have a large amusement park where $100 can buy an entire
season ticket and midweek visits have short lines.
However, I don't think she can force you to do a "trade" and allowing her to feel she gets to do whatever whenever she feels like it is not advisable. So okay to say No. As I wrote above, I don't know whether she can cancel and re-use her vacation time in the summer, a local lawyer can give local advice. The point is you have no incentive to be accommodative
when you have no expectation she will reciprocate similarly.
The members here have "been there, done that". I'll add that in most cases we who have faced high conflict relationships simply can't succeed when trying to walk an accomodating middle path. With BPD and other acting-out (Cluster B) personality disorders, being super reasonable and using reason — such as JADE (Justify, Argue, Defend, Explain) — doesn't work. The other person just can't or won't listen, at least not for long or consistently. Someone once explained it as there being too much emotional baggage from the past close relationship for the other to listen.
Best to limit communication to necessary parenting or schedule issues. Even that will be hard. Ignore the Blaming as best you can. A thought about boundaries... For a long time after I arrived here I thought boundaries were for the one misbehaving. However, in time I learned that boundaries were for me, my ex rejected them, almost predictably. How can that altered perspective help?
Limit conversations to necessary matters about (1) the children, (2) parenting schedule and (3) appropriate shared expenses such as child support, child care or daycare, etc.
That's where boundaries come in. When I first arrived here, I was confused, because I knew my ex never respected my boundaries. I learned that the boundaries were for me in determining how to respond to my ex. This is a typical pattern: "If you do or don't do ___ then I will do or not do ___." For example, "If you rant or rage on the phone then I will hang up." or "If you rant or rage then I will take the kids and leave to a park, restaurant or movie until you have calmed down." Frankly, your ex will never totally respect your consistent boundaries but over time it should reduce the incidents.
Be the parent with practical strategies and solutions. Yes, your ex won't appreciate them, but over time it can be invaluable in court and with the various agencies. Also, every time you're back in court be sure to attend prepared with the latest major issues and loopholes and their practical solutions. Even have them printed up as a proposed modification to the order, you'd be surprised how that forethought will give incentive to the court and lawyers to jump on it as a fix and ex probably won't be able to convince the court otherwise.
It is uncommon for children to be split apart between parents, shades of the "Parent Trap" movies. Be watchful for a solid legal opportunity to get the child 100% with her to have consistent time with father similar to the 5-5-2-2 schedule the other child has. I recall I had a magistrate who was fuming that her cases were backed up and she got peeved when I said something about what my son was slow to do. She retorted, "So is it up to your son whether he wants to go to school?" So ponder what H's son did, claiming he wouldn't go to school if he was with dad was a parental challenge that the law, school and officials would not have supported. It was brinkmanship, probably something he learned from his mother.
Review what I wrote above about boundaries. Don't be afraid to set boundaries. Ponder this... You're probably not a "black or white" person, you just have strong boundaries and a solid foundation in reality and common sense.
Similar for the college child. Probably an adult by now and so no legal parenting leverage for dad. Beware this is Guilting and Blaming. As in, I won't come unless I get my own room. Um, it's his father's home, father's terms. So don't feel Guilted, seems this disordered mother has taught a couple of her children how to be master manipulators. But that works only if you don't have boundaries and strategies to counter them.