Brothers of Fire

Set in the same world as the Familiar Mates series but following the royal phoenix shifters of Mont de Leucoy.

The Spy's Familiar is the crossover book in the Familiar Mates series. 

Reading order: 

Phoenix Spy (Dalmon) shop for the ebook
Phoenix King (Gerrit) shop for the ebook
Phoenix Mate (Kaine) shop for the ebook
Phoenix Prince (Everest) shop for the ebook
Phoenix Found (Olier) preorder