

Grady killed his children so also in Jack's crazy head he thought that Grady killed his kids because they were bad but if you remember in the beginning Grady the original caretaker simply went nuts and wiped out his entire family because he was nuts Danny was exceptional yes but more of a prophetic intuitive psychic type person slightly with multiple personality disorder. Yes Jack was talking to Grady prior to the door opening however there could have been a time lapse that is not expressively shown so this does not mean it was strictly a supernatural being or a ghost in the hotel who was able to move things remember Jack was also simply crazy and he was warned in the beginning everything in Jack's head was all delusional because of the warning he initially got when he was applying for the job everything else that happened thereafter was all delusions in Jack's head. First being that Tony forced Danny to unlock the door and then began talking to him letting him know that there was going to be something bad happening when he was screaming to his mom in the room right after the door was unlatched. Also this is a psychological thriller being with that everything that happened in the movie was all psychological delusions and no physical manifestations being manipulated by supernatural manifestations. If somebody was locked in the building along with the Torrance family most likely it would have been on accident and they would have crossed paths but this never happened so we can exclude that there were only three people in the Hotel. This can be deduced by numerous factors and reasons. it is my belief that Danny was possessed by his alter ego friend Tony who forced him to unlock the door.

after she locks him in there the next scene shows her and Danny in the room and Dann y screaming REDRUM over and over again. And ultimately escaping with Danny in the end. Obviously it was not Wendy as she was the one who locked him in there and she also remained sane throughout the entire movie. This is quite simple if you think about it.
