Stigmata by Rain Carrington

A thousand-year-old vampire is posing as a priest in an old mission to keep his stable of human cattle safe and happy. He feeds on them each evening and spends the rest of his time, well, bored.
With his three progenies, they are riding out the apocalypse with their own crop of food, hidden behind the high walls of the mission. When raiders come, the vampires protect the humans, and all that they need to give is their blood, though none know the truth of that except one.
One day, on a scavenge, Clarence finds a man on the beach, and the man is beautiful, strange, and overly eager to serve a mysterious master.
The man he finds is Grey, a genie, and that genie is about to touch all the lives at the mission. Caring, loving and kind, Grey knows he must serve a vampire, but the trick is, can he change a vampire’s cold heart?