8 books in series

The Guardians

The Guardians is a 9-book series with 8 released primary works first released in 1968 with contributions by K.A. Denver, Meljean Brook, Maggie Shayne, Marjorie M. Liu, Alyssa Day, William Joyce, and Wilfred McNeilly.

Forest of Ancestors
Wild Thing
E. Aster Bunnymund and the Warrior Eggs at the Earth's Core!
Toothiana
Demon Bound
Jack Frost: The End Becomes the Beginning
Must Love Hellhounds
The Haunting of Alan Mais
Demon Marked
Guardian Demon