Biologically speaking, which vampires make the most sense?

My friend and I spent a long time discussing the biology of vampires in different universes to see if any of them matched our "idea" of what a vampire should be.

Like, do the have blood? If they're dead, which means that their heart doesn't beat, why can you kill them by nail a stake through their heart? Their brain supposedly shouldn't work like human brain either, and since they also don't have a soul, how can they feel emotions? Depending on the universe, they can have children, but how? There's no blood rushing through their veins to, yk 📈