Help, this is a tough one. I read a series about 10 years ago (?) that had 2 books with a 3rd to be written. The story had a family returning to an island they go to every year for vacation. While the brother and sister are out walking near an old abandoned home they meet a girl in old fashion clothing. I believe the 3rd book was going to explain everything but I don't remember there being one or what the name of the series is. Does anyone know?