Orobas SPOILERS
I love how little this movie spells out for you.
The first time Molly hears something in the house, it isn't the father, it is a girl screaming and crying. She runs to the closet and holds her hand out in a trance. At the end, her older sister does the same thing. I think the father sold his soul to Orobas ( the room with the horse heads is a shrine or the very place he was conjured), and in turn the demon took his daughters souls too.