I didn't live with my mother as she was dipping into alzheimers. For some of it my father was around and for some of it, I didn't get it, though I visited, mm, 4 x week. It was when I took her to Boston (she was from Watertown) after my father died that I caught on. There wasn't any online then.
Indeed, my esteemed medical colleagues were no help. This was 1969.
I think, for now, you could be assertive to Mr. P, whom I've met twice and like.
Not sure how. Being assertive is not all that smooth a way.
I know that sometimes when seniors get into being difficult (now there's a word) things can be going on re meds and much else. I'm figuring you are looking at the morass of that.