Sounds like the oncologist won't let go until she gets her piece of the pie, sad to say. When I was diagnosed with a relapse after being in remission for almost 3 years, the multiple myeloma hit my hip and femur hard. I started getting calls from the radiation oncologist, even though I had told my nurses no radiation for me. Every patient is a potential financial bonanza, and if the doctors actually act like that is true, you really can't blame them: oh, yeah, except for the part about not having any ethics!
The decision about dad by the family is the right one and you should stick to it. Dad will not lose his hospice benefits for refusing multiple myeloma treatment. Your main concern is your dad, not the pecking order for the ambulance chasers.