Dr. centre here (haha)- what you’ve described sounds like classic long-lived narcissism, anxiety, and depression. Your dad has loyally chosen to remain in the marriage and this is just the latest chapter, your mom’s approach to life hasn’t changed, has it?
What is hard to accept is that in this situation, you have no power. Neither has been declared legally incompetent, so they have every right to make the decisions which we can all agree are problematic, and there’s the rub. You love them and see trouble here and danger ahead.
Google “loving detachment”, working at embracing that concept REALLY helped me when my parents were on this journey in their 90’s- unwilling to allow any help, cancelling anything we kids set up, etc.
I believe it’s a “treasures in heaven” moment to do things which are kind, which you really don’t want to do, so good for you for keeping in close touch with your mom. Do whatever you can to spend time with your dad.
Accept that you have no power, that this is a long-standing behavioral situation, and work at Loving Detachment. You’ll feel a lot better.