Books like Dragon War

The evil, immortal Boneless King has taken possession of the powerful dragon cauldron - with the soul of Thorn, the human child, trapped inside - and has declared all-out war on dragonkind. His plan: to use the cauldron to boil the seas and destroy the dragons. And he has convinced Shimmer's brother, Pomfret, to be his ally. The dragon princess Shimmer, the wizard Monkey, and Indigo, a human child, transform themselves into guards, horses, and even fleas to elude the despicable Boneless King. In desperation they return to the kingdom of the High King of the Dragons to recruit Shimmer's kinmates in a fight for their lives and to save the Inland Sea. Up high in the sky and down low to the underwater mountains they go to fight the Boneless King's army. Can they defeat this evil incarnate, return Thorn's soul to its human form, and restore the Inland Sea?