This conversation reveals just how greedy and manipulative Fanny is, and just how spineless John is. At the beginning of the conversation John is planning on providing for his step-mother and her daughters, as was his father's wish. But as his chat with Fanny continues, he is persuaded to provide less and less for them, and by the end he leaves them practically penniless. Truth be told, it doesn't take much convincing from his wife, which leads me to believe he never really wanted to provide for his step-mom and sisters. It could also be argued that he agrees to Fanny's wishes just to shut her up, which is just as spineless. He trades his honor to placate his wife, which shows that although in this world the men are in charge, the women can have power by pulling the strings from behind the scenes, so to speak.