Without my knowledge, my brother's paternal family, claimed him on their taxes. Now , my taxes were rejected, what can I do?

Are you saying you can legally claim your brother on your IRS return but someone else has already claimed him - and IRS didn't advise you that both returns (yours and theirs) are being audited?

Is there a support order? Who pays support for him? How old is he? If they do... they have every legal right to the deductions.

Judy and smoothy both raise valid points. You need to provide more information before good advice can be given.