Only one person may use a Battlenet account. You can’t log in to the account on multiple devices at the same time.
Your brother needs his own Battlenet account and his own copy of the game on each Device he wants to play it on.
Only you are allowed to access an account registered in your name. We don’t recognize the transfer of accounts between individuals. Activities performed on your account are your liability.
You may not share your account or password with anyone, except if you are a parent or guardian, in which case you may permit one minor child to use your account. You may not use your account at the same time, and you are liable for activities conducted by the minor child.
You are responsible for maintaining the confidentiality and the use of your user name and password. You are responsible for all uses of your information, even if you don’t authorize them. Security of your account is your responsibility.