Lingering Dead Birds questions

So I've read through a lot of these threads on the film and I still have some lingering questions.

1. Some people say that Todd had some sort of immunity from the demon forces because he had religion. So why didn't Sam's Our Father prayer and Bible citing have any effect?

2. If Todd could see the ghosts, why would he only be able to see the woman in the gross sacrifice scene but not the invisible perpetrator? Also, apparently what happened to her was a vision of what happened in history, but yet, moments earlier, the woman was talking to and addressing Todd….?

3. To that effect, as we saw Todd see other demons elsewhere, like the one in the barn rafters, why couldn't Todd see that the others had turned into demons?

4. Are we to believe that in just a few minutes after Clyde left the house, he was subdued by demons, gutted, stuffed with straw, had his mouth, eyes, nose, other wounds, etc. sewn shut with some kind of lace, and crucified? And apparently he was still alive and groaning, but when he fell down his head came off?