basically cultists have families and second born usually gets in the cult while first and third get sacrificed. Sacrifice can mean many things - in Cooper's brother's case they probably drove him to suciide - but also drugged and raped him in his sleep.
There's a lot to sahy about this but the victims don't actually know they are filmed, experimented on, or raped as the rape happens when they are asleep and they are kept ignorant of the rest.
the cult operates a symnolic existince communicating in poses, colors, and even things like hairstylels - they never say anyhting directly which is why there's no evidince - but they all still do things and operate as a cult because they speak that symbolic language and the victims do not.
as for the steps - the victim isn't given a real chance at life and has severe psych probleems (becoming things like school shooters) - but in between that they get uses for them - just give the kid a pizza and they'll eat it, and they won't ever know that in the middle of the night they got raped.
they also use nurseries, like this pic of Cooper as an adult - they do the same, drug the kids to sleep and then visit the daycares and rape.