My twit brother is having a few problems with his mac

1) we cant seem to get his mac to connect to our network, we use wpa-psk encryption and is there some magic trick to getting this trick to work.

2) my brothers airport gives off a stronger signal but i cant connect to it. so is there some way i can set his airport to connect to our home network and send out its own signal but leave our main router with its own signal so i can connect to it.