I watched the last exorcism and it didnt make sence?

i thought maybe i had it cause it seemed like she was trying to get the reverand to believe she was really possesed and she wanted him to take the baby out. but at the end i know the pastor was really an abalam worshiper and so is the brother. but was the dad and nell worshipers? and why would the pastor kill the demon child? im so confused help! :(