It is the house, but I don't believe it has soul unless soul and the spirit are the same thing. Maybe they're, maybe they aren't, whatever it is the curse of demons has been tied to the grounds around the island home. Father Marcus claimed the place is a demonic hunting ground, but if it is, it has shown over the years on holding the same pattern, with father going nuts and then murdering people cold bloodedly.
That is a very scary prospect, but it goes along the line of what we know about the haunted houses and cursed objects (see Annabelle). These places seem to become tainted over the years, maybe over milleniums, possibly going all the way back to rise of the man sixteen, eighteen thousand years ago. In theory, the Earth was pure, a paradise before it became tainted with pure evil and God didn't purge it from Earth. Instead, over all this time these immortal beings has hunted the mankind, occasionally possessing those with weaker mind and no faith.
In same theory all the people in the Island House should be susceptible for a possession, as the Father Thomas saw so many evil deeds surrounding the place, and so many of these people has been occupied by the demons. They don't blink or feel anything for committing horrendous acts as it has been with Andy and Truck, but afterwards these demonic victims go through terrible time, as they cannot understand how could they've done such things, because it's not in their nature.
The Exorcists must have iron balls for going at front of demon, holding their crosses and their faith alone, when the opponent is armed as it is with Andy's case. A normal man would have tried to disarm or disperse the population, by sending them out, but the Exorcist go with their faith. It is intriguing to see how that sometimes stop the possessed on their track, almost as if they're suddenly paralysed by the power of God.
Yet, we've seen the demons walking around sacred grounds like the Vatican. Why they can do that when they're so vulnerable to Holy Water?
