Stop using an account that's not in your name. Remove all ads. Now if the one who's name is on the account wants to use it, then give it to him. You never log into it again, nor let him log into it from the same browser you're using ever again. If the account would go unused if you don't use it anymore: delete it.
Now apply for your account under your name. One account, one person, one user. Add ads from the new account.
Even if Google doesn't currently go after people with two accounts, Google is known to change their ways sometimes (just ask those using Google Reader) and Google never forgets.
Two accounts that you log in from the same browser or that share an address, have their ads appear on the same website, ... will be labeled as "related", and if one of them gets in trouble, they'll block both in one go. Moreover the "you shall not have more than one account" is then used as a second offence and will complicate any restoration.
Simplest solution: forget about having or using more than one account.