What am I supposed to tell people when they ask, "What do your parents do"?

You doing fine with your response. "My parents were disabled in a car accident a number of years of ago." Is an adequate and genuine response. People ask that because they are trying to make conversation. Part of the strange look you get is them wishing they hadn't asked. You could ease the strain when they get "that look" by adding, "It was a long time ago. We've all adapted to the new and different rules of getting around." Then ask them something about their jobs or their garden or something that gets the subject changed.