My mother had a POA drawn up naming me & my brother agents. No one told me. He has been actively acting as her agent & hasn''t told me is this legal?

My brother has removed money from parents joint account and put it into one that I cannot even monitor the activity. Not knowing that she even had a POA my sister, another brother and I had a POA drawn up which my mother signed in an atty''s office, had notarized and witnessed, it does have a clause revoking prior documents. The ''bad'' brother hired an atty for my dad, atty says he''s not representing my mom and that the new POA is not valid. My mom was in the hospital then rehab and is now in the memory unit of an assisted living facility. She has not been diagnosed with dementia but has short term memory loss. My dad is in skilled nursing in same assisted living. He has cancer and is in hospice care. The ''bad'' brother has also finagled the other brother off of dads POA (other brother was not aware of being an agent either) and not told my sister that she is an agent on that. No transparency and very hostile brother HELP!!!