So the „hacker“ got your keys via Discord. Well, well, remember the very first rule, Steemit tells you when giving the keys to you?!

I cannot help you too much.
Your brother‘s recovery account has to initiate a recovery. In his case it’s @justyy. He needs to contact him. Maybe it’s possible via the website where he sells these accounts…
„Steemit“ has nothing to do with this case, since they did not create the account. @ justyy created it.

Good luck!