Sarah basked in Bradley’s protection and her adoptive mother’s favoritism. She told others that Avery was an unwanted child, and that her mother had taken her in out of pity, allowing her to live off others.

Whenever I returned home to complain about mistreatment, my mother would unconditionally scold me: “How dare you speak ill of Sara? How could you bully Sara?”

When Bradley came home from school and learned that Sarah had been wronged, he wasted no time and roughly pushed me to the ground: “Remember, Sara is my only sister. If you bully her again, I won’t hold back.”

I glanced at Sarah, who was basking in self-satisfaction....