The prolific Alice Hoffman’s new novel, “The Marriage of Opposites,” is a fierce, sorrowful tale of the conflict between personal desire and social constraints that echoes through three generations on the island of St. Thomas in the first half of the 19th century. Like her most recent novels, this story is grounded in historical events and assiduous research, but Hoffman goes a step beyond “The Dovekeepers” (2011) and “The Museum of Extraordinary Things” (2014) by taking real-life figures as her protagonists.