When Tessa Hulls set out to write a book about three generations of women in her family, she had few illusions about how hard the task would be. The tale was geographically sprawling, and spanned a century: Her grandmother Sun Yi, a journalist in Shanghai, fled China for Hong Kong in 1957, then slowly went mad; her mother, Rose, attended an elite boarding school in Hong Kong founded in part for the mixed-race children of European expatriates, then moved to the United States in 1970. Much of her family’s story…