Who is Mary and Bill from Z for Zachariah and what is their importance?

Mary and Bill are Edward's wife and son. Edward is concerned with the safety of his family when he realizes that a nuclear weapon has been dropped on Ithaca, New York. Edward wants to use the radiation-repelling suit to go find his family, but Mr. Loomis refuses to let him. In fact, Mr. Loomis shoots Edward and kills him before he can find his wife and child.