Although no where close to being friends, Bette and Joan find that they make a connection based on family, despite both having ulterior motives entering into making that connection. Part of the discussion includes Joan opening up about a sensitive issue from her childhood. The impetus for those discussions stem from three of their offspring being constant fixtures on set - Bette's daughter B.D. and Joan's twins, Cindy and Cathy - and their differing parenting styles. Bette, feeling that B.D. needs more of a focus in her life, follows Bob's lead, which may not sit well with Joan. Bette may regret her decision with regard to B.D., who she does not want to hurt, but who may prove a liability in the bigger picture of the movie. It is also not helped by Bette making a connection with Victor, who treats her more like a mother than his own mother when he gets into a bind. Despite that connection between Bette and Joan ultimately falling apart to those in the know, both Bette and Joan cannot help but feel that family is something they want to focus on outside of the movie. Part of that breakdown between Bette and Joan started before making that connection as Joan and Hedda were conspiring together to make Joan the star of the movie in the public mindset, Joan who alters the plan based on that connection and innocent comments by Bette. That breakdown turns physical on the set, especially as "Jane" and "Blanche" reach critical points in the story.
—Huggo