Isaac and Grandpappy?

Isaac was a demon tasked with killing sinners and evil doers, the house was essentially his courtroom to lay his judgment down onto the sinners, it disappears when he's handed down judgment and killed the sinners, which is John and Vivienne. Thats why the cop says its not the first time peoples came to her talking about a house that wasn't there.

They tell you who he is, he says sinners are drawn to him, he talked about the devil possibly having a son, he said he'd already been to hell. So you don't get concrete answers, but theres enough hints to put it together he's from hell and some kind of demon whos there to kill the sinners that are drawn to him like moths to a flame.

Grandpappy i think is just his helper, he told the family one day Isaac just appeared and he took him in. And at the end Jessica kills Grandpappy, but we later see him alive again with Isaac, cause they make a point to tell us "If you're righteous you will survive" so i'm guessing on those grounds only sinners can die. So i'm guessing those who are righteous if killed there are brought back once Isaac is done handing down judgement.