Elderly parent now rejecting adult children. Any advice?

Have any of you faced this situation ? I moved in with my elderly father nearly two years ago. Since my mother passed away four years ago, he has changed toward me, my children and two of my siblings. He only shows love to my older sister but it is almost to the point of unhealhy obsession. He is insanely jealous. If she and I talk he demands that we talk in his presence. If we go out together he becomes angry toward me as if I have taken her from him.
He treats his Home Health Caregiver better than me. In fact Ive learned that he has made it point to mention that we (me and my siblings) are adopted. I have a feeling that was he actually said was that Im not his daughter. This is so hurtful to me especially since his Home Health Caregiver is the last person that should know extremely personal information. She disregards anything I say regarding the household and now I know why because my father has made it clear that he does not view me as his daughter. He does not realize that she is the kind of person that will try to find a way for him to leave money to her if he should pass away. Im at a loss.