My ex stepmother is manipulating my Dad (90) financially and mentally! Any advice?

My dad was married to my 1st stepmother for 25 years, when she passed he was very lonely and remarried just a few months later. His new wife drained everything out of him financially and then divorced him. The problem is, they divorced over 5 years ago but she still is in change of his money and he told me she is paying her bills with it as well as his. The 2nd problem is she has brain washed him into wanting to be cremated when he already bought a plot next to my 1st stepmother. The funeral home sent me a cremation authorization to sign but why should I when he already has a plot. I believe she wants to sell the plot when he passes. Why else would she want him cremated? Also, she is already remarried to another sick/old man. She tries to keep the family away and tells him she loves him not us... meanwhile she divorced him!! This lady is a criminal but how do I prove it? She's been married several times and they have all been elder wealthy men. I NEED HELP! There is so much more to this story. I just don't know what to do. I want to stop her from doing this. I am his daughter. She is the ex wife! She has convinced him that he wants to be cremated when I know for a fact he doesn't and if I don't sign it he said he won't speak to me anymore! Please someone give me advise!