Love this movie... Like all Indy movies most of the characters and plot are up to interpretation of the viewer. Personally, I saw the story tellers as quasi "angels" but more like the good souls or souls of good parents/people who wanted kids but did not get to have them but still wanting to protect those they see as vulnerable.
The incubus are definitely the evil/demonic/self absorbed types who only use people for their own benefit.
Great story, ingenious cinematography