1. Send a letter to everybody to thank everyone includes A and his family for the opportunity to let your kid in.
2. Suggest another special test between your kid and A to determine who gets in the team if A wants.
3. If no answer after 2, just let your kid join the team and no need to worry about it anymore.
4. If A's mom still keeps bitch about that after 1 and 2, just give her a finger....