I was surprised they didn't play up the incest element more in this one. They way they portrayed it was almost gratuitous. If they had stretched it out a liitle longer, perhaps the possessed/touched sister was trying to seduce/corrupt the brother....somehting like that. The way it sits now it could have just been removed. It adds nothing to the movie. It's tittilating...but doesn't add any substance.
Did the inspiration come from the 2 film in the series? That's what I've always assumed.