You can have two accounts under the same address as long as you guys are two different people. Both accounts are sort of connected--if you get banned one domain, they will most likely ban the other (they will say you are related to another account holder's account who has been committing fraud or something, i don't feel like searching for it anyways). It would be wise to take care of BOTH accounts with a passion! Make sure no one does anything stupid since it can potentially hurt the both of you.
Plz don't play with adsense and got banned for ever !!! Many of my friends got banned and they can't even join another !