From reading your post, I think you're asking if you can take them all as an HQ choice. The box was brought out as an Apocalypse formation for the Space Marines, not as a codex unit. Using C:SM, they are each a Captain/Chapter Master model on their own, not a unit of 4.
If purchased as the Captain/Chapter Master, any one of them could be accompanied by a Command Squad/Honour Guard, depending on the listed option in the codex.
And a Captain is always good to have in an SM list.