In To Kill a Mockingbird, both brother and sister relationships of the Finch family share many characteristics, while, at the same time, there are some distinct differences:
From the beginning of the novel, it is apparent that Jem Finch and Scout are, like Atticus and his sister, loving siblings, although they do disagree with each other at times. When, for instance, Mrs. Dubose insults Scout as his "dirty little sister," Jem retorts to her insult. Likewise, Atticus insists that the children be respectful to their aunt and obey her. Both Atticus and Jem try to guide their younger sisters: Jem explains to Scout in the first chapters that her new teacher uses the new Dewey methods of education, while Atticus explains to Alexandra that he cannot face his children if he does not defend Tom Robinson and attempt to change "Maycomb's disease."
However, there is a difference between Atticus and Alexandra regarding their attitudes about the family name and its importance. For, while Alexandra feels that there is a distinct difference between the Finches and other families of Maycomb, Atticus is not so snobbish. Like Atticus, Jem and Scout agree with Scout's attitude that "There is only one kind of folks: Folks."
As the trial of Tom Robinson approaches, Jem and Scout do what they can to support their father such as come to the jail where the mob has assembled. Similarly, Aunt Alexandra is appreciative of Miss Maudie's defense of Atticus with her sarcasm toward the hypocritical Mrs. Merriweather after her remarks about Atticus's acting as defense attorney for Tom Robinson. Furthermore, Alexandra supports Atticus more as the trial progresses, and she becomes concerned for his welfare while Atticus explains to her the importance of upholding his commitment to justice.
In a parallel situation to Atticus's maintenance of moral integrity to his sister, Jem sets an example for his sister when he informs Atticus that Dill has hidden in their bedrooms on the night that he has run away from home. And, like Alexandra who tries to protect Atticus from insults, Jem defends Scout from Bob's Ewell's vicious attack.
The statement of Atticus Finch that the Tom Robinson case is "something that goes to the essence of a man's conscience" points to the greatest commonality of both pairs of brothers and sisters. For, they are all united in their sense of justice and morality and their love for one another.