If you have lost access to the account

Account Recovery
Make sure you are completely logged out of Steam before you start the recovery process

https://steamhost.cn/help_steampowered_com/en/wizard/HelpWithAccountStolen
https://support.steampowered.com/kb_article.php?ref=2347-qdfn-4366

When doing an account recovery, do not try to rush thru the process. Trying to rush thru normally results in information being missed and time wasted. Take your time and read everything.

Here is a guide that another Steam user was kind enough to make. It will help you navigate your way thru the recovery process if you are having any problems.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1126288560

While waiting for support to return the account, figure out how you gave away the account log in (if you havent already done so). All 3rd party sites are USE AT OWN RISK.


your brother needs to figure out how he gave away the log in. accounts dont get hacked, it is easier to get the account owner to hand over the information they need to steal the account