Also I don't quite understand what you mean. Are you saying that he can play from my former minecraft account if he wants but from a different username?
It's simple:
1. You should join with whatever name you used before - if not, you need to request a transfer.
2. Your brother should not know your /login password, and you should not know his /login password
3. Your brother's ign must be different then yours.
Oh I already got that covered. I already got on the server from my OG account. Thanks though, I lost all my items and houses... but the thing is that bugsy already teleported me to my old home and then she told me to go to my other main home using coordinates. I don't know how cords work but i'll manage.