In the game, we learned that the vampires reproduction is mainly through turning humans into another vampires by making them drink their blood, but Mary and Dr.Reid did not drink the blood of the vampires.As I understood, they both were just dried out of blood. So how exactly did they become monsters?
Spoilers. Stop reading.
Considering the time since you originally posted the question. You probably already have your answer or have lost interest.
The good doctor was bit and dried of blood by a vampire. His body thrown into a mass grave by undertakers. He was then chosen by a creature made entirely of blood who sired his vampire existence.
After unwittingly draining blood from his sister, the good doctor holds her close to his face. Her face pressed firmly to his wounded neck now flush with her own blood and that of the good doctor's progenitor.
The power of the progenitor's blood is enough to satiate a skal's appetite for eternity, create a vampire with a drop of blood placed on dead lips, and allow the good doctor to not have to feed on citizens.