Do you have a copy of this POA? sometimes these are files at the county courthouse, but there are no requirement on that. I am asking because I wonder if it is a "durable" POA?
Usually all POAs are null and void when the person who issues the POA becomes incapacitated, which would be the case if your brother is now in a coma. The only exception would be if the POA was specifically made durable, and this can be verified by reading the language of the POA, i.e. "this Power of Attroney is to expressly survive where I am incompetent or become unable to think or communicate," etc. If there is no such language, then the attorney-in-fact is acting beyond the powers of the POA, and as a relative of the person who issued the POA, you may have to instigate a civil suit to stop or undo what has happened.
Likewise, irregardless of a durability clause, what does the POA actually allow the attorney-in-fact to do? Most POAs have limitations written directly into them. Does this POA have any limiting language that requires the attorney-in-fact to act in your brother's best interests? It could even restrict the transfer of property or money to certain circumstances. Would the language as written into your brother's POA even permit the moves that have been made under that POA?
Violation of the terms of a POA can lead to civil lawsuits and sometimes, in extreme cases, criminal action.
Bottom line: get that POA, read it, and then see if what the attorney-in-fact is doing is actually permitted under the terms of the POA. You'll probably need to contact a civil attorney in your area for assistance on getting to the next step.