Why do u guys keep saying his friends don't like him I've had a similar problem though it didnt keep deleting my mates but they couldn't accept them.Check your and thier internet on the xbox network thing and see what thier NAT is cuz if it is strict it can stop them from accepting also check your parental controls (if you have got any?)cuz that can stop them from accepting.

Hope it helps

Opps this was quite awhile ago