"When they were children in the suburbs of Los Angeles in the 1950s, Diane Keaton and her younger brother, Randy, were best friends and companions: they shared stories at night in their bunk beds; they swam, laughed, dressed up for Halloween. Their mother captured their American-dream childhoods in her diaries, and on camera. But as they grew up, Randy became troubled, then reclusive. By the time he reached adulthood, he was divorced, an alcoholic,...