What is the plural form of brother-in-law?

Read this excerpt from we’ve got a job: the 1963 children’s march. then, in 1958, when he was nine, his mother got a job as a dental assistant – and a raise. at about the same time, wash got a job, too. six days a week for eight years, he woke up by four o'clock in the morning to deliver milk. by the time he got to school each day, he'd already put in almost half a day's work. how does this excerpt readers make a personal connection to the story? by connecting readers to his mother’s medical training by connecting readers to the milk-delivery business by connecting readers to wash’s academic success by connecting readers to wash’s daily work routine