I read this book in the early 2000s, it probably came out between 1997 and 2002 although I'm not sure. The main characters are two siblings (maybe twins, I think brother-sister). Their village/town is overtaken by an army and forced to march to a distant city as slaves, although one of the siblings escapes. The siblings have some sort of magical connection and the plot revolves around the escaped sibling trying to rescue their family/village. I do remember there was a whole thing about the people who got captured being surprised at how they were treated relatively well when they got to the city of their captors, who seemed to have some sort of ulterior motive (other than you know, the slavery). I did not find out what this was as I was not allowed to check it out from the library and finish it, and it has been haunting me for two decades.