Okay, so equal parts Saw and Psychovile? ….I’ll buy that book from you. You can officially consider me a fan.
I agree the plot can be tricky. It sounds to me those two don’t have a story as such, unless you want to make a point about what they are doing. I’m not so sure you should. They found a rather strange hole in the market, they are filling it, and from what you told here they should to be as satisfied with life as any person can expect to be.
It might be easier to do chapters on their clientèle. What they want, why they want it and what happens when they get what they want.
Oh and I think you need a government official antagonist. Someone from the health department or ethics commission or something, whose life’s work is to shut these people down.
And a lawyer who has a barter agreement with them.