Me and my brother use the same steam account but recently he had to go to USA and now we are not sure what will happen if he uses the account there and it activates some sort of anti piracy mechanism and bans our account. I live in Turkey.
1.C. Your account:
When you complete Steam’s registration process, you create a Steam account ("Account"). Your Account may also include billing information you provide to Valve for the purchase of Subscriptions, Content and Services and any physical merchandise offered for purchase through Steam (“Hardware”). You may not reveal, share or otherwise allow others to use your password or Account except as otherwise specifically authorized by Valve. You are responsible for the confidentiality of your login and password and for the security of your computer system. Valve is not responsible for the use of your password and Account or for all of the communication and activity on Steam that results from use of your login name and password by you, by any person to whom you may have intentionally or by negligence disclosed your login and/or password in violation of this confidentiality provision. Unless it results from Valve’s negligence or fault, Valve is not responsible for the use of your Account by a person who fraudulently used your login and password without your permission. If you believe that the confidentiality of your login and/or password may have been compromised, you must notify Valve via the support form (https://support.steampowered.com/newticket.php) without any delay.
However, Steam has a built-in Family Sharing system in place to share games between family members.
It allows one game to be shared among multiple people. Read up on the conditions so that you don't trigger a ban.
Note: Steam can easily tell when you login from a different country. When I go between Hong Kong and China, it kicks in an extra verification when I login. If you do this and, for example, perform a login from location A, then 10 minutes later login from location B half way across the world, that's gonna be a ban right there.
Even if you use a VPN, there's no way you can pick a VPN server that's close enough to bypass geo-location detection. You'll have to run your own VPN server where your brother is logging in. At that point, just setup a free second account for yourself and share the games.