Error while registering. Need help!

I want to register with my account: bdegrote.
But it says: ''You may only register one account!''
But that's the account from my brother :/ .
And I want to play with my brother on the server.
How can I register without this stupid error?

Try registering from another IP address like your friend's house.

use a computer different from the one your brother used to register

ill register you, ill send you a private message with the password for the acc "bdegrote"