How can I get my father's caregiver to move-on?

I do not live near my father but I expect to be living with him soon. Due to my father's physical and mental conditions he hired a female caregiver through a service over a year ago. After a few months the caregiver convinced my father to buy-out her contract because it would cost him less and allow her to administer his medications. My father is now lonely and unhappy with his situation The caregiver has isolated my father. Her salery is very high (Dad is "not sure if he is paying her $45,000 or $60,000" per year). A few months ago she stopped being there 24/5 and is now with him less than 40 hrs per week (without a reduction in pay). She convinced my father to hire her son to be with him on weekends however, he cannot stand her son. My father has always needed a woman in his life to nuture him. He has taken a shine to this caregiver who is 30 years younger than he is. She has my father convinced that she has professional medical experience therefore, he considers her to be his personal lifesaver. She changes his medications without doctor authorization. He helps pay her rent and bills, buys her furniture and buys groceries for her family of five which she cooks at his home to take with her when she leaves. She sold her vehicle and commandered Dad's car 24/7 which leaves my Dad and her son stranded together on weekends. There have been times when she has scammed my father for cash for herself and her friends and family. Her sob stories of how broke she is and how hard her life is makes Dad want help her so that she will be happy. Dad has recently included her in his will so that she will have hope for a brighter future. He hates to see her weep at work and allows her take daily naps to regain her strength. Because she is so stressed-out she yells and argues with Dad and her family (via cell phone) when she is around. She has told my Dad that he has physically and mentaly abused her and he is confused by these comments. I could add more but, I think the picture is clear enough for most of you to see that Dad is a victim of elder abuse..
Adult Protective Services has investigated and recommended to Dad that he get different caregivers but he just belives that APS, her former employer, the police and the only family member he had near him are "out to get her because they don't like her". She turned my Dad against the only family member who could advocate for him and threatened to have her son's beat that person up. Her son's are violent and do have criminal records. My Dad want's me to help take care of him and I will. However, he won't even consider getting rid of his female caregiver. California authorities would like to arrest her but they don't have enough evidence to prosecute and my Dad protects her. Does anyone have any advice for me?