Your sister if she is capable needs to be pushed to get a GED and work doing something. She should have a drivers license even if she doesn't have a car to drive. She should be contributing in one way or another, even if it's cleaning grandma's house.
Your mother has skills, even though they might not be past job history. Is a cleaning service a possibility? Maybe have it be a business for your mother and sister?
Her cleaning skills are masterful. I guess that's 33 years of being a homemaker. I have definitely suggested this before.