The killer cant be who they reveal it to be SPOILERS!

So the realtor's wife was the killer and her son was the kid who burned down the house ten years ago. I can buy that. What I cant buy, is how she is able to be in two places at once. The most glaring mistake is when she is in bed with her husband, he gets called to the house and heads right over. Yet she is there waiting for him in the basement. How did she get there so fast? Faster then him?

Second, after the realtor and his wife, drive away when the others arrive, they take the same car. When the 2 cops are killed -by her- she is then seen at home in bed with her husband. Wouldnt he notice that she was gone? Do they have 2 cars?

Third, this is minor, when the guys first arrive, someone yells "Get out" through a vent. Yet, the wife is in the car waiting for her husband. In fact, she honks the horn for him to come outside. How could she do that?

As laid back as I am about slasher movie storylines, this one drove me nuts. Its like they werent even trying.
I like guns, slasher movies, and more guns.