If my brother is capable of making decisions, would his medical power of attorney be allowed to decide on personal medical procedures?

The doctors and personnel should not even be discussing brothers medical with older brother. His POA should read "when principle is not able to make his own decisions" unless immediate. If your brother is not happy with older brother he can revolk the POA and assign someone else. That would solve his problem.

You would need to review the original, signed PoA paperwork to know exactly what language was used and what authority was given to your older brother in the PoA. You can look at your disabled brother's original copy and may be better able to come to a conclusion. If older brother is not adhering to the signed agreement then disabled brother can discuss or revoke the PoA and assign to someone else who has wisdom and can be trusted not to create a power struggle over him. Good luck.

I copied this for you. And you are correct, the brother you are caring for would have reached a point where he is unable to make decisions for himself before a POA kicks in. He would have had to sign something for this to make your other brother the POA. "A medical power of attorney form, also known as an “advance directive” or “health care proxy”, is a form that allows a person to elect someone else to handle health care decisions on their behalf only if they are not able to do so themselves. The situation that would require this could be due to any type of incapacitation events such as a coma, vegetative state, or any type of mental condition that impairs the principal from thinking rational. The document must be signed in accordance with their respective State laws which require either witness(es) and/or a notary public to acknowledge the signatures of the parties."

I feel for you, I have an older brother the same way..