My father might be showing some signs of senility. He is in his late 80s, my mother in her mid-70s. The main problem is that in the past month he has become increasingly stubborn and impulsive and is insistent on doing things that we think exceed his physical capabilities. He won't sit still for a minute and is constantly hatching plans - in the past week every day he has planned some kind of (relatively) strenuous outing often going well into the evening. My mother cannot talk him out of doing these things and when she tries he gets very angry and belligerent. She is very scared that if he goes out on his own like this something horrible will happened, so she feels compelled to accompany him - he threatens that he'll just go alone if she doesn't want to join him. He completely denies that his has physical, let alone maybe mental, limitations. My mother is absolutely exhausted and can't take it any more. I live far away and have small children and am becoming overwhelmed with anxiety on my mother's behalf and guilt too for not being able to help her more.
What can/should she do? How do we cope with this?