What has stopped me going down legal route is that they could set in place everything in the world but she has a knack of playing the emotional "don't worry about me i'll be fine on my own" card that always makes the kids (especially my eldest son) stop & question what they are doing because they feel their mam is unhappy.
The courts could put everything in place but if they can't stop that i'm losing every time.
HI Buddy.
just to say on the above issue that you really need to do the tough love thing with them again. That whole sense of emotional abuse that your x is using is not on and you need to empower the kids to stand up to her. Its abuse.
You sound, from the stuff you did with the school, that you have a good head on your shoulders and can come up with ways forward. I would encourage you to talk to them, esp the boy and ask how he feels about it when his mum says this kind of stuff. Talk to the school, who sound like they are on your side! Talk to the Dr again to as emotional abuse could lead to depression etc and the Dr may have some advice or be able to sign post you on. I know i keep using the emotional abuse phrase but dude it is!
If you go down the legal road you might actually empower your kids to see they have a choice. Plus your x will have the opportunity to have her say during the process and your kids will see that. They will also see that actually she WILL BE OK and they can NOT WORRY ABOUT HER, she's a grown adult. They might see the courts ruling as a rubber stamp that she can cope without them and they can alway trump her with "but its the courts ruling we have to go see dad!"