Bone Quill
John Barrowman and Carole E. Barrowman Audio Book

12-year-old twins Matt and Emily Calder are Animare: they can bring art to life and enter paintings at will. They must do everything in their power to prevent a breach in Hollow Earth: a supernatural place that holds all the demons, devils and creatures ever imagined. The Hollow Earth Society are getting closer to finding the key that will release the beasts: an ancient bone quill whose powers can be only be used by a powerful Animare. The quill has been lost for centuries, but important clues to its whereabouts lie somewhere on the island of Era Mina - as does the entrance to Hollow Earth itself. Matt and Em must find the quill and protect it - but their lives in the relative safety of Auchinmurn Abbey are thrown into confusion with the arrival of a newcomer who threatens to ruin everything they have worked for. All too soon, the twins are forced to make a terrible choice: save their father, or save the world.