Deathspell - Veronica Stallwood

Hanna Benson is a lucky woman, with her large house on a wooded hill overlooking Oxford, her rich and successful second husband, Malcolm, and their five children. Anyone would envy her. Any outsider.
But when Malcolm begins to lay down the law, Hanna's ten-year-old daughter Tess decides to fight back. She wants her family together again: just her, her little sister, her mother and her real father, Gerard. There is no place in her world for Malcom and his three vicious sons. And it seems that Gerard is only too willing to offer Tess her paradise - he provides her with the perfect way to achieve her aims. Murder.