In the last couple of years, my mother and father live in the same household, but have been estranged off and on over the years. My father in the last decade has battled diabetes and recently, he became a dialysis patient. Recently, he left my mom to live with my uncle. He has named my uncle as the POA and my mom is very upset. They have been married for 50 years, in a community property state.
Note that Uncle cannot make any decisions for Mom.
I think you need to stay neutral about this if you want to retain good relationships with both parents.