If you just lay all the Show/ Tell/ Expert things into three sequential chapters, I think that’s excessively linear and dull.
What you could do though is ask some leading questions then let the variety of answers from those categories fill in the responses. In each case, perhaps a different aspect of the triad would lead the exploration.
For purposes of illustraton, let’s say this was going to be about Steve Irwin. No reason, just go with it.
Example topic: “Kids”.
Some b-roll “show” with voice-over from “tell”, cutting to and from on-camera interview sources from Tell section, describing the couple’s ideas about their own childhoods, child-rearing, setting limits and laying out examples and giving inspiration, then a confirming opinion and anecdote from the outside “expert”. In Steve’s case, (and this had to be dealt with in an actual documentary on the subject) there was a lot of agonizing, introspection, and re-assessment going on after the “holding your baby too close to crocs during a public performance” affair.
The doc used b-roll of Steve interacting with the kids, his own and others, intercut with the controversial footage, then up-close interview footage of a discussion of the affair afterwards, sort of a post-game analysis. The doc did much to rehabilitate the late Irwin’s career after massive negative world press from the baby-croc affair, and Irwin’s star was again in ascendency when he unfortunately met the stingray.
It’s the hopping between past/present, and subject/evaluator perspectives that fills out the idea of what happened and how people thought about it then and now, how it changed them. I liken this mode to how the cubists like Picasso sought to try and show multiple perspectives in one 2-d image, to make, not anything photo-representational, but something that really evoked the inner nature or character of the subject. Done poorly, it’s a jumble; done artfully, it’s more than it was before.