I believe my mothers caretaker is coming onto my father. Any advise?

My mother has dementia and my father is not able to take care of her..they are both 89. Dad, I think, is of sound mind and body. A caretaker was hired to take care of my mother..she is a very capable, attractive 30 years old. I have POA, but he and I got into a very big arugment (I am 70) .. I was taking up for the caretaker before other things came to l light. She lives downstairs and is full time. There is no privacy and she reports everything any of the siblings say to my father to one sister who is causing problems with all of us. I have been told to leave and never come back. I am not allowed to see my mother. My brother dropped in to see dad around 9:30 pm, just walked in as usual..the caretaker was sitting at my fathers feet with a very slinking nighgown on with much of her chest showing...he did not say anything to my father, because ..well, you have to know my father . He is very controlling and stubborn. He told me he took away POA, although I have not heard from anyone about this except him) and I cannot do anything. My mother is being put to bed very early and the caretaker is calling the house hers ... we are afraid he is about to be taken for a ride. The sister he talks to the most is a very good friend of the caretaker and is told every thing we say to dad..the sister is a taker and owes my dad thousands of dollars .. she had POA of my uncle and took $90,000 before found out. My father knows this, and Im not sure he trusts her, but the caretaker and sister are in cohoots. we do not know what to do...sounds like a soap opera doesnt it....but it isnt, and Im sure this has happened before. Any help out there?