So, how exactly did the horse die? Also, what was exactly the train of thought for the family to believe the father killed the horse? He had to drive up to the house, get out of the car, get the horse out of the stables, position it somewhere on the driveway, get back into the car, drive up to the horse and somehow hit it, and then drag the horse to the pool. While being drunk. What?
It's presumed it was hit by a car, had its head bludgeoned (as happened to Dale's family) or had its throat slit. Maybe the family thought the horse got loose, or was out in a field overnight?
IIRC the family believes it's the father precisely because his headlights/front of the car is smashed. The implication being that he hit the horse with the car. Which is illogical once you start thinking about it. Especially the whole 'getting a dead horse into the pool while drunk' part.
Why did the husband leave his wife alone in the woods, at night, during the rain near the well with dead bodies, knowing well that there is a killer out there?
He was trying to get better reception on his walkie talkie to alert the sheriff, and he didn't know the killer was in the area.
Where the hell did the killer go after pushing the wife down the well? Why didn't he proceed to push down the husband?
The husband was trying to get better cell reception, so he wasn't near the well when his wife was shoved in.
So, Dennis Quaid character... He has no friends whatsoever or what? Why couldn't he call his best friend in NYC or something? At least to share what's going on, and maybe ask for a little assistance, especially after sending away his family...
It's implied that Cooper realizes what happened with Dale's family immediately after his own family left, and Dale attacked within the following 12 hours. I don't think someone could fly out from NYC and come help him within that timeframe.