North! Or Be Eaten: (wingfeather Series 2)

Janner, Tink and Leeli thought they were normal children, but now they know they're really the lost Jewels of Anniera, heirs to a legendary kingdom across the sea, and suddenly everyone wants to kill them. In order to survive they must flee to the safety of the Ice Prairies. First, however, they have to escape the monsters of Glipwood Forest, the thieving Stranders of the East Bend and the dreaded Fork Factory.
But even more dangerous are the jealousy and bitterness that threaten to tear them apart, and Janner and his siblings must learn the hard way that the love of a family is more important than anything else.