1 Grace's husband died
Grace’s husband died while he was fighting during the World War.
2 The ghosts are the humans
Grace and her kids were afraid of individual people and thought that they were ghosts. These were the people who recently moved into their house, but they were ordinary humans.
3 Grace killed herself and her kids
Grace did not know how to deal with the situation after her husband's death, due to which she killed her kids first by strangling them under the pillow and then committed suicide.
4 The new servants were ghost
Grace thought that new servants came to help her. However, they were new ghosts as they were also already dead, who were living in that house before they used to live. (See Ouija: Origin of Evil (2016) Movie Explained)
5 The old servants disappeared
The old servants disappeared from the house when they found that Grace's family is no more. However, Grace thought that they disappeared because of an unknown reason as she did not know the entire truth that she and her whole family were dead.
6 The kids were not sensitive to the lights anymore
The lights used to affect the kids earlier when they were alive, stopped affecting them now after they died. (See The Devil’s Candy (2017) Movie Explained)
7 The husband must haunt the place he died in
As soon as Grace's husband said goodbye to his family, he left the house and could not return to the house. Maybe because he was supposed to haunt the place he died in.
8 Grace family is destined to haunt the house
The sole reason was that Grace’s family died inside that house due to which they were supposed to haunt the house.
9 The humans tried to talk to Grace’s family
The humans tried to find the reason why other spirits were haunting the house. They were doing this by establishing contact with other spirits, along with Grace and her kids. This scenario demonstrated why Grace saw the old Psychic lady once who was having the same face as her daughter.
10 The family thought they were alive
Grace and her kids thought that they did not die yet, and they were living just like ordinary humans. They were also afraid of other ghosts who were turning out to be like humans.