She’s seen paternity battles, struggles for alimony, vicious tugs-of-war over children, but veteran family attorney Susan Bender had never handled a custody fight quite like this. A gay male couple donated sperm from one of the men to a lesbian couple, resulting in a baby. Each couple bought identical New York apartments and decorated them exactly the same. The intention was to split the year into four quarters and rotate the primary parenting duties amongst themselves. The complex plan was intended “so that they could all parent the child or children in some meaningful way,” the attorney said. “They were...