Key moment in Three Wives, One Husband (Channel 4): Enoch Foster, a fundamentalist Mormon, has gathered his two wives – Catrina and Lillian – and 17 children for a meeting in one of their houses blasted out of a rock in the Utah desert. For the past months he has been courting a potential third wife, the nanny Lydia Rose, and he wants to propose. It’s a family decision though (he says); he’s putting it to the vote first. Yay, they all say, everyone puts their hand up … Oh, except for one little boy.

“Joseph, do you want Lydia to be your mom?” asks his dad, in a way that strongly suggests the correct answer is yes.

“No,” says Joseph, shaking his head.

“Do you want Lydia to come move with us, to live here?” Enoch asks again. Still Joseph shakes his head.

I like this kid. He’s actually thinking for himself, not doing what’s expected of him, and he knows he doesn’t want another mom. Maybe, someone should go and rescue Joseph, at least take him to see The Book of Mormon, I think he’d benefit from it.

Actually, the kids seem to have a pretty nice time at Rockland Ranch – mucking about outside, tobogganing, jumping into the pool (filming happened over a year). It’s just what goes into their heads I worry about a little, as well as the number of moms they have.

The film is a mixture of hand-held filming with some fixed-rig, observational with some gentle interviewing. Objective and non-judgmental. I imagine an awful lot of time and effort went into developing a relationship with and gaining the trust of the community. And it pays off, they clearly do trust the crew, and open up, their homes and their lives. Express their doubts, even – especially Enoch’s second wife Lillian, who admits it’s hard to watch her husband falling in love with (yet) another woman. Yeah, actually, Lillian didn’t shoot her hand up either at the vote. To be honest, if they actually thought about it, probably the only person really keen for Enoch to marry a woman who is about 20 years younger than he is Enoch. And God of course, polygamy is a way to get closer to him and reach the highest level of heaven.

Apart from the fact that it wouldn’t have happened any other way, the documentary’s trust-gaining softly softly approach doesn’t make it any less extraordinary. It’s pretty much one long OMG WTF. The setting itself is so brilliant. I had questions about the houses, such as why make them house-shaped, with pointed roofs, when they are set into the cliffs? What about services, plumbing etc? And are they not a little dark inside, with aspects on only one side? I guess when you’ve got three wives, and God, you might not be so worried about that.

Enoch is an odd one. Wheelies seem to be his thing, on the trail bike, on the quad bike, with a wife or two or a future one (he hopes) on the back. They seem to be impressed: oh, Enoch, we love your massive wheelie, whose turn is it to bear you another child? Now he’s John the Baptist, in the water, dressed in white, dunkin’ children.

Facebook Twitter Pinterest Abel and family in Three Wives, One Husband Photograph: Vance Jacobs/CHANNEL 4 PICTURE PUBLICITY

Other things are almost normal. Like Beth next door going off to work in a local bank, and Suzie training to be a nurse. Beth and Suzie are married to Abel, who’s also married to Marina, who’s pregnant and stays at home to look after the children (11 so far). I wonder if there’s something of that to Enoch’s quest to marry again, keeping up with the Morrisons?

Also, with polygamous marriages, there are not a lot of single men in the community, beta males who get to marry nobody, possible because they can’t do long wheelies. Maybe they just wander off into the desert?

So the vote; and little Joseph eventually changes his mind, or has his mind changed for him. His hand goes up, Lillian’s too. It’s decided, Enoch can buy the ring, thank God (they do, amen).

Oh, but it turns out Lydia isn’t sure she wants to marry Enoch after all. Maybe it’s the age difference, or the big wheelies didn’t do anything for her, but she’s not 100% sure she loves him. What? What’s that go to do with anything? It’s God’s will.

• This article was amended on 27 March 2017. An earlier version referred to a “trial bike” where “trail bike” was meant.