Alright I have a theory ready, Nick is half demon - which is why his mother always stares at him so.... horridly. Her life is some how tied into his - maybe if she dies he'll turn full demon or something. Which explains some of his more...violent nature and serious rage issues and probably why everyone seems to think he's a psychopath - He clearly has feelings there just... not as intense or easy for him to reach as everyone else, due to the whole demon thing.
I'm guessing his demon father? looks a lot like Nick, which might be why the female demon always seems to think he's someone else?
One problem, Alan is older so how was Nick conceived if the mother was no longer in the circle?