Yes, you can. However, you must have a power of attorney to be able to take care of his tax issues. Your brother must file Form 2848 with the IRS- it will authorize you to deal with his taxes.
Here is the form and it's instructions:
https://www.irs.gov/pub/irs-pdf/f2848.pdf
https://www.irs.gov/pub/irs-pdf/i2848.pdf
