You said you are not the administrator, but you didn't say whether an administrator has been appointed. If an administrator has been appointed, the administrator is responsible for all tax matters related to your brother's estate, including the final tax return, if one is required. You don't have to do anything about taxes.
I assume that your brother had some assets or possessions, and may have had some debts, even if only recent unpaid bills. Since he did not have a will, if no administrator has been appointed you should consult an estate lawyer about having yourself or someone else appointed as administrator to pay any debts and distribute any assets.