You are facing a very difficult situation, I know, because you don't want to meddle in your parents' lives or make the situation even worse than it is.
But as parents grow older, sometimes the roles they and their children once had become reversed. In other words, the children have to step in and become the "parents," and the parents slowly but surely become the "children"–dependent on their sons or daughters to take care of them. From what you say, this may be the situation you and your brother are facing.
I'm not a doctor, of course, but clearly something serious is happening to your mother, and she needs professional diagnosis and care. If she doesn't get it, the situation may only get worse–and the burden on your father will grow even heavier. Let him know you are concerned for both of them, and because you love them and want what's best for them, you will help him get medical attention for your mother. Together you can do it.
The Bible says, "Honor your father and your mother, as the Lord your God has commanded you" (Deuteronomy 5:16). This commandment isn't just for us when we're young; it applies as long as they live. Ask God to give you wisdom as you seek to help your parents, and to honor Him–and them–by your love.