If you are playing offline on your brother's account on your PS4 while he is also logged into his account on his PS5, kicking him out of the online session would not be possible. Being on different consoles and playing offline means you are not connecting to the game servers, so there is no way to actively interfere with his gameplay. However, if both consoles are connected online, it would be possible to kick him out if you have administrative privileges on the game or console.
