...I would back way off now, even more than before. Let the people who get paid deal with him. And take care of yourself best you can.
When I realized my NM was a sadist-- that she really did derive pleasure from my pain, it was devastating. How could anyone be that way, but especially a parent toward their child? Unfathomable, really.
It just showed me, though, how disordered her thinking was. How far removed from my reality she was. It was like she was on another planet, some alien being that could never exist in my world.
Once I was able to swallow the truth-- and it was very difficult to get it down-- I was able to view her with an empathy I hadn't had before. I knew she truly was a N, because a hallmark of narcissism is lack of empathy. And I knew beyond a shadow of doubt that I wasn't a N.
When I went NC with her, I didn't look back. I had tried so valiantly to care for her, in vain. She was always going to view me as less than my GC brother, who was selfish and ruthless and only cared about her for her money and his inheritance.
It's hard to let go of illusions, but when reality sets in, it does allow one to operate in the confines given and let go of any hope that the narcissist will somehow mellow in their old age.