House of Angels — Freda Lightfoot

The Lake District, 1908.
It seems as though Livia, Ella and Maggie Angel lead a charmed life on a large country estate. But since the death of their mother, their family home has been far from a quiet haven as their bullying father is determined to marry off the girls to his greatest advantage.
When the sisters discover their father had an affair many years ago, which resulted in the birth of a baby girl, they determine to find their half-sister, and their search begins in the local workhouse. Mercy had been unaware of her connection to the rich Angel family until her mother's death-bed confession, and once she knows, she's not at all sure that she wants to be part of the family after all.