If your brother is an adult, and he is poor and you have the sufficiency of means, then you should support him from other than your Zakah funds.

 

If the above is not true, and the only way you can help him from your zakah funds, then you are certainly allowed to do so – since he is poor and eligible to receive Zakah.

 

As a matter of fact, in this case, you will merit doubly rewards: reward for giving charity and reward for helping your kith and kin.