My parents are both retired. My father is 70 and my mother is 67. Both have health issues. My father takes care of the finances, however, he has stopped paying all of their bills. My mother is going blind because of an eye disease (maculardegeneration?) and my father is not paying any of the doctor bills. Eventually the doctors will refuse to treat her. He hasn't paid any of the taxes on their house in several years. His creditors are taking legal action. How do I go about declaring him financially incompetent?

You will need to go to an attorney to start with, you will have to file a motion with the court to have someone appointed a guardian over them

I would start with his doctor. His doctor can help you assess his capacity.