Take action on the clear-cut stuff. Leave the emotional blackmail stuff for another time:
1.) File a grievance with the sport association that accepted a fraudent waiver. That will ensure they do not do it again and it will eventually involve her because she knowingly signed a legal document for a minor she has no legal control over.
2.) Submit a written statement to his school notifying them that she is not his legal guardian and can have no involvement in his education decisions or progress. For example, topics discussed during conferences are private and can be protected. Also ensure she is not on any list of approved adults who are allowed to remove him from school (i.e. for doctor's appts). Now, what they cannot do is prevent her from attending special school events like a carnival or music program.
3.) Do the same with his clinic, his dentist and his healh insurance carrier. You are within your rights (HIPPA) to prevent her from attending his medical appts or requesting his files.
4.) Amend the custody agreement to document that exchanges will either be done in Outfit XYZ only or that anything on his person or in his bag during an exchange must be returned at the next exchanged with little to no damage. If not, monetary recompense will be made.
5.) Amend the custody agreement to include specific lifestyle issues that must be mediated and supervised by legal parents only (i.e. hair cuts, religious observance, sleep-overs with friends, sports, scouting, piercings, music and viedo games, movies, holiday observances (i.e. mom picks the halloween costume this year and dad the next).
6.) Work with the school to ensure a copy of all projects, assignments, events, etc. goes out in two sets (one for mom-one for dad) to ensure no more things like the "My Family Poster" happen again.
7.) Amend the custody agreement to cover communication during extended absences. For example, when on vacation in FL, child will call mom 2x a day to check in.