It doesnt look like you were willingly sharing your account. But, realistically it doesnt matter. The account compromised was the correct thing to do, you will be unbanned at the next restart as soon as someone can get to it.
If you did happen to willingly share your account (which would be very stupid) you are still responsible for anything that happens under your name. So if your "brother" gets you banned you will still have live with that.
Just some food for thought, keep your password safe and secure, dont hesitate to do /logout