it's not possible, and if it were, blizzard would either suspend or close the account. Their user agreement states only one person to an account, only one person uses the account, only one character can be logged into at a time... so theoretically if you could get 2 characters online with the same account, it'd probably raise a red flag on blizzards systems and they'd have a coniption fit

my brother used to share accounts with people though lol but he would get booted from his friends when they wanted to play though lol