Sister World: The Arrival - Sister World, #1

The first of the Sister World Trilogy, Sister World , The Arrival, tells the tale of the dangers faced by the people of Terah.  Existing in an alternate universe, Terah, a mirror image of Earth, has had a very different existence. Since the terrible conclusion of their second world war, the free people of Terah have been forced to remain in hiding, resisting the brutal control of Frauliege.  When the alternate universe and the means to travel is discovered, Frauliege knows that she can now conquer two world.
 In resistance headquarters, two teens learn the impending fates of both worlds.  With their armies pinned down and no one else free to make the journey, they brave the wormhole and begin searching for their mirrors, hoping to not only save this strangely similar world, but the family that would be theirs.