All That Will Remain. Books of Furnass, #9

It's 1914, and the Lyle family, like the United States itself, is at a crossroads. Malcolm Lyle, all too aware that he is no engineering genius like his father who founded the company, has made the Keystone Steam Works internationally known through his abilities in marketing and adapting his father's ideas. Now he must decide whether to devote the company's resources to a lucrative government war project, or to back his son, Augustus, who is an even worse engineer than Malcolm, in the development of the ill-fated steam-powered Lylemobile.
Meanwhile, he learns that his youngest son, John Lincoln, has gone off unannounced to join a multinational effort to fight the Kaiser's invasion of Europe, at the same time that the boy's unmarried twin sister, Mary Lydia, turns out to be pregnant. Malcolm's wife, Missy, is no help with his dilemmas, content to spend her days dressed in peignoirs and lying around on the living room sofa reading women's magazines and eating bonbons.
His eighty-nine-year-old Mother, Libby, the steely matriarch of the Lyle clan, watches Malcolm's every move with what he believes is an unapproving eye. Then there is Libby's Caribbean maid, Perpetual, an impenetrable figure with a room full of medicinal plants and an indelible, irrepressible spirit, who has inadvertently become the axis around whom the Lyle household revolves.