I see everyone is going the vampire route on this one and I, for one, hope you're all wrong. It's such a tired genre.
I was thinking (hoping), based on Dad backstory and glowing eyes, that maybe what we have is a genetic enhancement, drug-induced perhaps, introduced at early stages of various characters' lives and then possibly passed down as a persistent genetic mutation. That could be in keeping with the need for "specialized" marriages, to test and/or magnify the effects of the mutation.
Since at least the Mom (Elise) seems to have the precognitive power, I was hoping that was a logical extension (no precog vampire powers, to my knowledge). The red-eyed Caitlyn does present a possible problem with this theory, but, hey, genetic mutation could merely have branched in her case, possibly telekinesis or other form of mental mutation.
Hope it's not vamps or shifters, but even if, hopefully not MC, at least.