Olivia Havilland didn't talk to her sister for something like 60 years. They insulted each other , and Olivia I think didn't invite her to her mother's funeral. Joan was told she could not use her own last name, de Havilland, because her older sister (The favorite, I guess?) in Hollywood. Olivia is still alive, and living in France, but I am not sure she was Melanie in real life.
Speaking of Joan Fontaine and Joan Crawford, they were in a movie called The Women about this kind of behavior. I believe Stage Door. was another such movie.