How does Harper Lee develop the relationships between the members of the Finch family?

Harper Lee uses both the everyday events of the Finch family and highly dramatic events like the trial of Tom Robinson and Bob Ewell's attack on the children to highlight the relationships between Scout, Jem, and their father, Atticus.

The more pedestrian moments of life in Maycomb, Alabama, are portrayed by Lee to show the development of Scout and Jem's relationship. They attend the same school not far from their home, and the older Jem advises Scout on his experiences with certain teachers and in different grades. They walk to school together and often return together (until Jem reaches a grade that requires him to stay later than Scout). They attend functions on the school grounds, as when Scout has a part in a pageant at the school the night Bob Ewell attacks Scout and Jem.

In the summer, Scout and Jem often play together with their visiting friend from Mississippi, Dill, and engage in occasional mischief. Jem emerges as a protective, loving brother to his little sister, though at times he grows irritated with her behavior and questions, just as she at times becomes exasperated with Jem's moodiness and superior attitude as the elder sibling. They share almost all of their young lives with one another and are close siblings, despite their different genders and ages.

Scout and Jem look to their father for guidance in all areas of their lives, and Lee reveals Atticus is a firm but fair father.

The crises of Tom Robinson's trial and Bob Ewell's attack on the children bonds Scout, Jem and Atticus beyond the daily events of their small-town lives. Scout and Jem see their father as heroic in his defense of Tom, including an evening prior to the trial when Atticus sits watch outside Tom's cell, employing his moral presence to fend off a group of vigilantes intent on killing Tom.

When Jem suffers a broken arm defending Scout from Bob Ewell, Scout wakes up the next morning to see her father faithfully watching over her brother from the same chair Atticus occupied the night before, never having left his son's bedside.

The Finch family is bound together by genuine love, reflected in both the quotidian passing of the days and the dramatic events of lives darkened by sometimes difficult and dramatic events.