How can I find out the name of attorney who executed my mother's P.O.A.?

My mother lives in New Hanover County, NC. My brother, who lives in Washington, NJ is her P.O.A. My mother expressed concern to myself and my two sisters that she had" concerns" about some of the things my brother has done. She stated she wanted my brother's P.O.A. rescinded, that she preferred to make my sisters Dual P.O.A.'s. We took her to an attorney in NC to discuss this. He stated that rescinding her P.O.A. had to be done through the attorney who executed it up in New Jersey.My brother will not tell us who that was. Where do we go from here?