You and your brother were sharing accounts for quite some time, while either he or you claimed this was false it was only a matter a time until it became too obvious for not to be seen. Now it is your chance to come up with the truth and accept that you made a mistake, because you knew very well that multiaccounting is forbidden, I'm sure this was told to both of you when you registered your account.
Until you're not willing to accept this there wont be any way for you to get unbanned.