I dont think their vampires I think their some kind of humans who have been turn into demons/monster
Or things pretending to be human. They kinda remind me of how monsters used to be represented in folk stories/myths and old legends. Where monsters were always disguising themselves and tricking ppl right up until they kill you.
My theory early on was the town was trapping families going through trauma or just gone through trauma but this flashback kinda threw that out. Seems like it's just pulling families or close ppl (a$$hole engineer dude was with his bff) that on the road? Not a lot of common denominators