How did Ali become a part of baba's family?

Chapter four opens with the story of how Ali became a part of Baba's family. In 1933, the same year Baba was born, two intoxicated young drivers struck and killed a Hazara couple. Only their five-year-old son, Ali, survived. Baba's father was asked to decide the young men's punishment. After sending the young men to serve in the army, he took Ali into his household. Baba and Ali grew up as quasi-brothers, just like Amir and Hassan a generation later. But despite their closeness, Baba never considered Ali his friend just as Amir never considered Hassan his. According to Amir, their ethnic and religious differences kept them from being true friends or family. At the same time, all these years later, Amir says Hassan is "the face of Afghanistan" to him. The boys played and got into mischief together like any other two boys, except that Hassan made Amir's breakfast, cleaned his room, and did all his other household chores. While Amir went to school, Hassan stayed home to do housework with Ali. After school, Amir would read to Hassan, who loved books despite his illiteracy.