Nana and Pop Pop

 

John and Doris Jamison, otherwise known as Nana and Pop Pop, are the main antagonists in the 2015 horror/comedy film The Visit, which was written by M. Night Shyamalan.

The Visit
After Rebecca and Tyler's mother sent them to live with their grandparents for a week, they were advised by their grandparents to never go into the basement because there was mold in there, and that their bedtime was 9:30 PM. One night, Rebecca discovered that Doris was projectile vomiting. When she confronted her grandfather about his wife's  condition, he warned her to not leave her room after 9:30.

Throughout the week, Nana and Pop Pop act even more strange. For example, Nana began to shake violently when Rebecca asked her about what happened on the day her mother left, and they were shown as being very hostile to a woman they had been counseling. They led the woman away to an unknown place, and she was never seen again (though it's later revealed that they murdered her, and that they left her body to hang from a tree). Tyler and Rebecca decide to use a second camera so that they could record any unusual happenings downstairs, and Nana finds the camera, and she tries to break into the kids' room, knife in hand.

After they had recorded the footage, they contacted their mother, Paula, and she reveals that they weren't their real grandparents. The two siblings try to escape, but the impostors force them to play Yahtzee. Rebecca excuses herself from the table, and she goes into the basement. After rummaging through a box in the basement, she finds the corpses of the real John and Doris Jamison  dressed in their mental hospital uniforms, thus implying that the impostors were escaped mental patients.

Pop Pop discovers Rebecca in the basement, and he locks her in a room with the disturbed Nana. He then started to psychologically torment her younger brother by smearing his face with his dirty diaper. Rebecca manages to stab Doris to death with a glass shard, and she runs into the kitchen and tackles John. When John was starting to get the upper hand, Tyler attacks him and knocks him to the floor. He then proceeded to repeatedly slam the refrigerator door onto the fake John's head, thus killing him.

The film then ends with Paula reuniting with her children.

Trivia

 * John Jamison is portrayed by Peter McRobbie, while Doris Jamison is portrayed by Deanna Dunagan.
 * According to some of the dialogue, John and Doris murdered their actual children, put them in a suit case, and drowned them in a lake. Their envy for what Tyler and Rebecca's actual grandparents had was part of their motivation, aside from being completely insane.