Audrey has been many different people during her years in Haven but this, finally, is her original personality: Mara. She and William actually created the Troubles she's been trying to solve for years.
When Duke asked Audrey to reactivate his curse, he didn't count on the curse changing. According to William, Duke is now filled with all the curses that his family has ended over the years. He's dying from the inside out. And fast.
It must have been hard for Nathan to head butt the woman he loves but, at the time, there weren't many options left. Audrey was about to give him a second Trouble. Let's hope she doesn't end up with a broken nose.
Dave and Vince are adopted brothers but no one knew that Dave was from another dimension until now. The thing is Dave doesn't want to get back to that other dimension. Ever. He even tries to shoot Vince to keep it from happening.
Jennifer, like Dave, William and Audrey, is from another dimension. And those are the four people needed to open the portal back to the world they come from. Jennifer used the book, Unstake My Heart to open the door but she immediately regrets it.