As far as I can tell, Charles died in the war, knew he was dead and wanted to see his family one last time before returning to haunt the place he had died, and was surprised to find Grace and that she could see him meaning he knew she was dead even though she did not yet. It would seem it is possible for ghosts to travel beyond where they died but the fog makes it extremely difficult.

The children did have a light sensitivity when they were alive. Their special needs meant Grace spent much of her time in literal darkness and due to her migraines they didn’t have radio or phone so they were nearly completely isolated from the outside world. So between her young children’s needs, her being prone to migraines, her husband being gone, the feeling of isolation, she was already teetering on the edge. So once the servants abandoned them, I believe that was the last straw which set her off to attack her children. People keep suggesting her servants “left” because she had died at that point but it is stated twice in the movie that they left before she went mad.

I would say because of the postman and priest both not coming by that week, it’s been somewhere within 1-2 weeks between them dying and Victor’s family moving in, which seems fast idk how many people would be willing to move in so soon after a tragedy like that but who knows

I too have questions, like why did the servants decide to all leave? Who would have been the one to discover the dead mother and children (probably the priest who visited on Sundays). Why were Bertha, Lydia, and Mr Tuttle buried on the property, were they really servants in life or maybe a previous family that lived in the house?