Ok so I have to ask at this point because I might be reading it wrong but, skeptic!Apo au is Pyro in anyway apart of the poly relationship forming because of his weird third thing with Apo that feels like it would bleed over to Cherri and Abolish if given the chance (there is already an ask that confirms that they think Abolish is hot) or no?
Are Apo and Pyro involved? Yes. Platonically? No. Romantically? Also no.
Pyro is schrodinger's polycule member. He's not involved, but he's also not not involved. He's not dating any of them, but Cherri and Abolish aren't dating each other, so clearly that's not mandatory (/j)
I think the best and funniest way to explain it is through how I see their living situations. Abolish has his own apartment that he got partially through the organisation. Cherri has her own apartment. Pyro and Apo share, and have no plans to change this. There is no endgame where silverhellfire all move in together, they would actually dislike living together I think. If anything, Abolish and Cherri become platonic roommates and Apo keeps living with Pyro, because if Abolish and Apo tried to live together they would have a category 5 clutter incident and leave no survivors and they both Know This. (Apo removing the silver from the watchtower made Abolish so mad he had to go to the mines to cool off. they could NOT live together. INCOMPATIBLE!)
Pyro and Apo aren't dating but they ARE stealing each other's clothes and this DOES result in Pyro wearing Abolish's and Cherri's clothing too (because Apo stole it, and then Pyro stole it from her) so from the outside it definitely looks like it. However if asked if they're together Pyro would go "she wishes" and Apo would go "ew. no." and then Pyro would be offended she went "ew" and elbow her in the ribs and get his arm punched.
in conclusion Pyro is in the polycule but his title is "Apo's roommate"