The officer, Beulah
These two characters aren't quite characters. We don't have any idea what they are like. They are in the story to help us understand the other characters. If we didn't know that the officer was in the navy and therefore moved around frequently, we wouldn't understand that the woman probably married the narrator in part because he promised a more fixed and stable life. Similarly, we wouldn't understand that Robert is deeply sad and grieving if we didn't know he had just lost his wife.