If joint POA, how to remove one son?

I am a bit confused by this post. I hope that you find a solution to your situation soon.

Not sure what the question is...are you asking if one of two sons who are both assigned PoA can be removed? Only by your mom by creating a new PoA, or through a the courts, a legal process. Someone can pursue guardianship of your mom but that is also done through the courts. It depends on the circumstances and the laws in her state. It sounds like you need to consult an elder law attorney.