A Simple Vow,in the Simple Gifts series, by Charlotte Hubbard
Edith Riehl longs to be a mother, but is unable to conceive. Asa Detweiler asks her to take care of baby twins while he looks for their real father. Edith's father thinks Asa is the father who abandoned the babies. Asa is determined to clear his name. What is the heartbreaking deception they uncover?