we have faced a similiar situation in the family and sadly theres really no way to solve it without someone getting butthurt
what we did was install those camera things like the ring doorbell discretely in the main rooms, kitchen living room etc. made the family member watch their own behavior several times then used the video to show the doctors and ultimately get the old man medication etc
i will find out what cameras they are, if youd like. you could even watch and hear in real time on your phone whenever you wanted and gave mom(who knew the cameras was there) a "safe" phrase she could use if she need us to call in law or someone.
bad thing is now the old man has passed and i am afraid my wife has installed them here to spy on me!
