I’m sure this is just a PR act of unity, intended to placate angry supporters of the other candidates, save face for the candidates themselves and let the establishment know that Trump doesn’t totally reject them . But it’s only that - PR (And a smart move I think.) That’s not to say the eventual VP isn’t on the list, only that not all 5 of those, barring unforeseen developments, is really contending.
Those are the only people Carson knows. He lives in his own little box.