Yes!
Since your mother is of sound mind, your mother can revoke some or all of any power of attorney at any time. She can revoke part of your brother's power by giving you the power over the one account, which would be a later power that conflicts with an earlier power. She can modify all of it by signing a new power of attorney. She can revoke the prior power of attorney altogether without giving anyone else a power.
The form of the power of attorney is not as important as its content. Let your mother decide how she wants all of this to operate and have her update her estate planning documents, namely, the powers of attorney as soon as possible.
Sincerely,
Kevin Spencer
(214) 965-9999
www.spencerlawpc.com
Answered on Jan 19th, 2015 at 1:07 PM