In confused as to why you are trying to change schools. If your current school doesn't have clubs/sports then enrol your children in after school activities. Ask your hubby's opinion on activities before you come up with a decision and he might be more responsive.
Lawyers seems like an over reaction unless the new school is really highly rated. Even then talking to your ex before decisions are made surely would be preferred. Ie take it back a notch: forget the school thing for now. Open up the conversation with your ex about how to address your sons anxiety. He might have some good ideas that don't involve up-rooting the kids from their school.