No you can't when it is a account for your brother whos the only Person playing on this, but when you and your brother share a account you will get in danger. And two accounts on one Pc is (when i know correctly) impossible because the Webside prevent User from having multiple accounts :<
If you two stay on your own accounts, then it'll be fine. Account sharing, on the other hand, is not allowed. So if you stay on your account, and your brother stay on theirs, nothing will happen. In the rare case something does happen, shoot an email to accounts@ppy.sh.