The question is specifically about the vampire aspect (MC is a vampire)
from what I've managed to gather from google and the rather awesome Theoi.com, there are a few ways I can adress this:
both are underworld demons/spirits. Empousai tend to be more like the boogymen and devour whole beings, where Lamiae (and were more often than not once human) were actually seducers that drank blood
I'm leaning towards more the Lamiae, and have vampires (a particular clan of) once be the spawn of Lamiae
BUT Theoi.cm points out that later authors took off from there, tending to write Lamiae as more ghosts or phasma (wiki points out that apparently the spirit in the movie Drag Me to Hell is a Lamiae, but /shrug)
the MCs would be Third and Fourth generation from the original Lamiae
My question is
Does this seem like it could work, myth-wise?
Or can anyone point out a better myth/reference?