I'm sorry that you have such challenges in your family.
I'm confused why there would be non-real doctors seeing her. In the US doctors have to be licensed. Do you have a sense that there are unlicensed doctors practicing in your area? What would they think is wrong, that they couldn't help with at all?
I still get the sense that your father wants attention and his "teasing" your mother is how he gets it. And your mother feels her role is to be the family support so she takes the teasing and tries her best to care for the house and feed the family. So both are locked into patterns that they've been in for so long that they don't even think about them any more. They are just what they do. It's like walking the same path to school every day for years - after a while you don't even see the path any more. It is just the way you go.
Your two real options are to work to change it, or to find a way to be at peace with it. Either you try to reduce it, or you accept the way it is. If your path is to feel upset every time it happens, that's just not healthy for you.
For your grandmother, it sounds like she has a powerful reason to be at home, and probably nothing else will ever "come above" that in her mind. So, accepting that, the best path seems to be to do the best to make the home stay as gentle and pleasant as possible. Maybe a nurse can visit once or twice a week, and help her that way?