Sisters Grimm series, by Michael Buckley

Sabrina and Daphne’s parents disappeared, and in the past year they’ve become experts at running away from bad foster homes. When their grandmother (whom they thought was dead) shows up and takes them to her home in the upstate New York town of Ferryport, the girls get ready to run away again. Then they discover that they are the last living relatives of the Brothers Grimm, famous journalists who exposed the doings of fairy folk before they were shipped off to live in a magically enclosed community in America. Some of the fairy tale characters are friendly and helpful to the girls, but there’s a secret society amongst them that is dedicated to destroying the Grimm family, and they have stolen the girls' parents. This is an incredibly exciting adventure story featuring two wonderful, smart, complex little girls.