I am caring for both of my parents. My brother wants to control their assets, kick me out and put them in a home. What can I do?

I am caring for both of my parents. They are 91 years old. Dad has begininning stages of dementia and moms heart is failing. They own a few paid off rental houses and the one we live in. My oldest brother is durable power of attorney and got my folks Dr to write a letter saying both are not competent to handle their finances. They are competent. He wants to control their assets, kick me out and put them in a home. What can I do?