I’ve admired and even adored most everything she’s produced until now. “Next of Kin” is a new memoir that purports to examine some terribly upsetting episodes: the suicide of Hamilton’s eldest brother, the sudden death of another brother and Hamilton’s various estrangements from every single member of her family. But despite a deep well of material, “Next of Kin” lacks the force and vision of her previous book, and its parts fail to cohere.