The House in the Cerulean Sea

I always include major spoilers (hidden), to help with my memory  issues. Read them at your peril! 

Linus, a Repressed, but decent man working for a grim magical supervisory department is  sent to a mysterious far away island. Here he finds 6 especially different magical children Lucy (Lucifer), son of the devil; Talia, a gnome; Chauncey, a jelly-fish-like creature who wants to be a bellhop; Sal, a frightened and damaged shape-shifter; Theodore, a wyvern; and Phee, a forest sprite. Two adults care for the children Arthur, who eventually turns out to also be magical, a phoenix; and Zoe, and island sprite. Linus is afraid of them all at first,  but gradually loosens up, and helps them to branch out as well. Tension introduced by way of hostility from bigots in the nearby village.