Is it possible to stick to a fixed schedule excepting emergencies? Having some ground rules might help about switches.
I have a friend who's parents had divorced. He wouldn't go to his dad's house because he felt better/secure at mom's. While that respects his POV better, I wonder if it caused resentment or just an empty love bank.
Result? His connection with his dad disappeared and when the dad died, he only had one son at his death bed. While the dad may have had it coming, as your W may, I wonder if it affects my friend's relationships with others.
Once a schedule is made, the kids need to feel they aren't pawns in a game by your W. That they are loved by both. A flexible schedule might get that, but then again, love includes committment.