Night's Temptress by Mary M. Cushnie-Mansour

Seventeen years have passed since the events of the "Night's Vampire Trilogy." The children are now of age to take the final ceremony, forever binding them into the dark vampire world. With the full transformation of his children, Basarab is almost ready to pass the crown to his son. Santan knows it’s his destiny; however, he’s hesitant, for he holds a secret in his heart that calls him away from the vampire throne. Samara, on the other hand, is determined to do whatever it takes to be the vampire ruler.