Introduction:
The change in the brothers' behavior towards the sister is caused by the realization of his mistake and the desire to make amends. This is the correct answer because it aligns with the events described in the passage and the character development of the brother.

Explanation:
1. The realization of his mistake:
The brother initially mistreated his sister and acted in a mean and hurtful manner. However, as the story progresses, he begins to realize the consequences of his actions and the pain he has caused his sister. This realization dawns upon him when he sees his sister crying and upset because of his behavior. He starts to understand the impact of his actions on her emotions.

2. The desire to make amends:
Once the brother realizes his mistake, he feels remorse and a strong desire to make amends for his behavior. He understands that he has hurt his sister and wants to rectify his actions. This is evident from the fact that he tries to comfort his sister and apologizes to her sincerely. He also promises to be kinder and more supportive in the future.

3. The intervention of their parents:
Although the parents do play a role in the story by reprimanding the brother for his behavior, it is not the main cause of the change in his behavior towards his sister. The intervention of the parents serves as a catalyst for the brother to reflect on his actions and realize the need for change. However, it is ultimately his own realization and desire to make amends that drives the change in his behavior.

4. The narrator's insistence on reconciliation:
The narrator does play a role in advocating for reconciliation between the siblings. However, it is not the primary cause of the change in the brother's behavior. The narrator's insistence serves as a reminder to the brother of the importance of repairing the relationship with his sister, but it is the brother's own realization and desire for reconciliation that leads to the change in behavior.

5. The brother's fear of consequences:
Fear of consequences may initially affect the brother's behavior, but it is not the main cause of the change. The brother's change in behavior is driven by his realization of his mistake, the desire to make amends, and the understanding of the impact of his actions on his sister. Fear of consequences alone does not lead to a genuine change in behavior.