Fields of Grace by Kim Vogel Sawyer

With their eldest son nearly to the age when he will be drafted into military service, Reinhardt and Lillian Vogt decide to immigrate to America, the land of liberty, with their three sons and Reinhardt's adopted brother, Eli. But when tragedy strikes during the voyage, Lillian and Eli are forced into an agreement neither desires. Determined to fulfill his obligation to Reinhardt, Eli plans to see Lillian and her sons safely settled on their Kansas homestead--and he's equally determined that the boys will be reared in the Mennonite faith. What he doesn't expect is his growing affection for Lillian--and the deep desire to be part of a family.