Abby's twin 's sister situation was not resolved. We don't even know how she disappeared.

Actually there is a sequel to this about the twin and Conner, and it HAS been made into a manga, but it isn't on this site for some reason. It is called The Bride Hunter. Wish I could find it, but I think I would have to look on Renta and I don't have the money for that.

There are also 2 prequel BOOKS in the series about the two older sisters, Mia and Lizzy (The Girl with the Golden Gun and The Girl with the Golden Spurs, respectively), but I don't think they were ever made into mangas.

And I was only able to get up to part 6...