Atticus and Aunt Alexandra, for being related, are incredibly different. Atticus always tries to see the good in others, and see things through their point of view, and wants his children not to judge others by what the people of Maycomb say about them. Aunt Alexandra is a judgmental gossip, and wants Scout and Jem to find themselves to be better than others, because they are Finches.
Despite these differences, Atticus and Alexandra have a mutual respect for one another, and Atticus wants Alexandra around so that she can teach the children how to behave in a certain manner (since this is what she wishes to teach them).
Scout momentarily thinks this difference may have come from some kind of magic like that in the fairytales that Jem told her.
