So what I know about the Pokédex holders is that most or all of them have roles or jobs, just like the members of the Order of the Stone. (Minecraft Story Mode fans would understand.) The roles for the (new!) Order of the Stone are:
Jesse the Architect (leader)
Petra the Warrior
Lukas the Author
Ivor the Alchemist
Olivia the Redstone Engineer
And Axel the Rouge.
I might add some of these in as Pokédex holders later on. But for now, I have Jesse and Petra.