Sorry, but all I can think about is Flounder in Animal House telling everyone he's a legacy.
This kid could DEFINITELY change over the summer - puberty is a strange and wonderful thing and sometimes takes its time happening. Also, have you met him on his own, or has it always been with his dad or brothers in tow? He might be feeling so much pressure from them that he can't loosen up and be himself.
Just try to look at him as another guy and not a legacy - that's the best way to give him a fair shake. Oh, and if after all this you don't give him a bid, DEFINITELY call the alums in person to let them know. One of our chapters dropped a double (mom and grandma) without telling anyone and let me tell you, grandma was one angry woman. It's WAY easier to do damage control before bids go out than after..