The Hendersons aren’t cursed; they are mimics. They learn behaviors by watching. When they stand facing the wall, they are learning to ignore the world. The wife does the same because she has been "watched" long enough to imitate them.
This is the true genius of the "Neighbors Curse." It isn’t cursed. But it makes you curse your own curiosity. You read it. You look out the window. You see nothing. You look again. You see a shadow. You realize the shadow was always there; you just never paid attention. That is the curse. The lack of an official ending has turned the fanbase into detectives. The three most compelling theories are: neighbors curse comic
Don't look.