What steps can/should I take?

My divorced father was recently diagnosed with early onset Alzheimer’s and vascular dementia. He is no longer allowed to live on his own and has been staying with my family. My mother, his ex wife has been getting involved with his finances (what little there is) and going so far as to hide conversations with him so that I can’t see them. I have so many bad feelings about her intentions, and I have asked her to please stay away and quit calling him etc. I feel like she is leading him on, as he started wearing his wedding ring again. I don’t know if she is doing it to get what little he has left or whatever, but she is telling him that she will help him sell his big possessions etc. What if any recourse do I have to make this stop, since she will not, even though I have asked her multiple times.