What is never touched on in the film is the cult's recruiting methods. New recruits are led and mentored by existing members, but there is no indication of HOW exactly the new recruits are convinced.
When Martha is showing Sarah around the farmhouse for the first time, she introduces her to one of Patrick's babies. Sarah asks if it's a boy or a girl, and Martha says "Patrick only has boys". Think about that for a second.
Patrick has sex with all of the women in the cult for purposes of procreation and encourages all of the members to be polyamorous, but it's never mentioned whether Martha was impregnated by him or anyone else and, if so, what happened to her baby.
The cult has some very peculiar ideas about death, so much so that they think death is beautiful, and that when you kill someone they don't really die, they just continue existing in another dimension. Now look at the previous two entries again.