This is a new series. Kinda like the extension of the 39 clues. The sort-of prologue book is called Vespers Rising by Rick Riordan, Peter Lerangis, Gordon Korman, and Jude Watson. It's like a transition between the 39 clues series and the Cahills vs. Vespers series. Here's a list of the authors of the upcoming books of the new series:

Book 1- Gordon Korman

Book 2- Jude Watson

Book 3- Peter Lerangis

Book 4- Roland Smith

Book 5- Linda Sue Park

Book 6- David Baldacci

So yeah. Can't wait for the new series. Remember when Fiske Cahill mentioned another family wanting Cahill powers? Well, you're looking at 'em. More info about the Vespers is in the Black Book of Buried Secrets by Rick Riordan.