Dawn Schafer, Undercover Babysitter by Ann M. Martin
Dawn has a busy summer ahead, spending time with her family and her friends. Then the BSC land some rather difficult new clients: a feuding family searching for a treasure that will settle a strange will. Now Dawn is even busier. She has to take care of her new charges...and she's determined to see that they patch up the feud. Maybe she'll even solve the inheritance mystery!