i can't give medical advice, i'm not a doctor.

not saying this is what's happening to your father but my mother in law started to develop dementia and she would repeat the same things and became very difficult to "manage". started mistrusting everyone and eventually she had to live in a skilled nursing facitliy. so it seems you need to get your father to a doctor but if he's competent in the eyes of the law there's nothing you can do to make him go unless you get him declared incompetent. it seems your mother can't deal with this and your're very busy and out of town. any friends or relatives that can step in? i assume not otherwise you wouldn't be in this position. Can the GP make a house call? Off the top of my head sometimes churches, etc.. are a starting point for advice, even an attorney. And of course the GP. Best of luck, your're in a tough situation. Lurking had some great advice.