I actually think Nathan was supposed to be the "Evil one".

Looking at his biological father, you might be right. Though I'm still trying to work out the logistics because that guy sounded like he was on the Rev's side, just as well as Simon Crocker.

With Duke's trouble revealed, it's now clear what he can do. Audrey might even be one of the first troubled persons ever - we don't know how old she truly is - and it might be her who brings the troubles and they vanish with her, like you said. But when she is there, her "power" you could say is stabilizing things, helping the people get through the troubles more or less unharmed.

So what does Nathan represent? His trouble per se doesn't answer the question. It would kinda make sense if he could start troubles, trigger them, bring new ones.

Then we'd have one who starts it, one who ends it and one who balances it out. But somehow, I don't think that is Nathan's part either. Hm.

It's a really fascinating concept if you get down to it.

That it is. Like I said, I'm not usually a fan of "love conquers all" but in this case, it would be so fitting and wonderful to see it.