The Last Exorcism questions?

Okay, so me and my friends just saw this movie, and I was just a little confused. I get that the demon impregnated (what's the girl's name again? Nell, Jell? Bell?). Were those people around the fire at the end a Cult? I get that they threw the evil baby inside her into the fire, killing the demon. I think those drawings on (Nell's ?) walls were ones she drew, but only after the demon impregnated her with the tainted baby. But why did the brother kill the camera man by decapitation? And why did Cotton's other friend get killed? what I'm saying is, Why did the drawings come true?