Which Way Round the Galaxy by Cressida Cowell

The O'Hero-Smiths may have rescued their little sister Annipeck, found K2 and Izza's father Everest and triumphed over the robot assassin called the EXCORIATOR - but their story isn't quite over yet. Because there is danger and possibility in the Which Ways. And a new adventure bursting with magic is about to take them through the crossing points and into new worlds.