Continuity mistake: In the scene when Dalton is climbing the ladder trying to turn on the light in the attic, it shows him stepping onto the same step twice.
Continuity mistake: In the scene where Dalton screams after falling off the ladder, when Josh runs to the attic to make sure he is alright his shirt is untucked with no tie. However when in the attic his shirt is buttoned with a tie.
Visible crew/equipment: When Josh goes to 'The Further' to look for Dalton and goes up to the attic where the red door is, the room is filled with an eerie smoke, but as the camera pans out a little, you can see the smoke machine in the bottom left hand corner billowing it out. (01:18:50)
Continuity mistake: In the scene where Renai is listening to the baby monitor, she drops it when the voice screams, "NOW!" On the floor, the speaker is facing down, but in the next shot, it is facing up. (00:22:35)
Continuity mistake: During the gas mask scene, Elise screams and Specs pulls off his headphones. The headphones knock his glasses off. However in the next shot his glasses are on. But then in the next shot he is picking the glasses up and putting them back on. (00:56:55 - 01:04:15)
Continuity mistake: In the scene where Mom and Dad are in bed and there is a loud knocking on the front door, if you look through the window behind the bed, you can see daylight and what looks like a parking lot. When the father is walking down the stairs, the light from outside is blasting through a stained glass window. Then when he goes to the front door, it is pitch black outside. He then turns on the porch light and the bulb burns out. At the end of the scene, they show the entire front of the house, and the porch light is on.
Visible crew/equipment: When the dad goes to wake up Dalton, he bends down to get some clothes for school, and you can see the audio wire.
Continuity mistake: At the beginning of the movie when the mother Renai is in the kitchen with the kids, there is a black square in the wall. But when the father Josh walks into the kitchen, the square has a wooden board over it.
Continuity mistake: The mom and dad are discussing things going missing around the house. The coffee table in center frame goes from having one toy snake on top to also having a plush turtle and toy robot on top. Then back to having just the toy snake again. (00:12:17)
Answer: It's implied that the girl went crazy and killed her family, but it's not really elaborated on. They're just some of the many spirits to be trapped in and haunt the Further, likely due to the violent nature of their deaths.