I have watched 'The Others' with Nicole Kidman last night, great movie however one thing that I don't understand is if they all are ghosts, how does husband fit into this?

I mean he presumably died in the war so how come then he returns home and then leaves again? I thought ghosts were only people who have died in the house (or the island), does that mean that anyone (dead) could show up?

Another thing is why is he in the movie at all? He does not add anything to the plot in my eyes only confusion, I must be missing something obvious here.