If Sanji and Zoro fight Sommer and Qillingham, it's probably gonna be like vs Kaku and Jyabura, where they could fight them, but not really damaging them enough because of Tekkai. Here we have more or less the same situation, in this case their immortality is the ''new'' Tekkai. I don't think they are gonna struggle much against them in combat itself, but actualy damaging them. But once they can get through it - with their new PU, ''controlled'' ACoC - it's gonna be over quick.
But the bigger problem here is HOW Sanji is gonna unlock it. I once wrote a post here, how difficult it's gonna be to give Sanji CoC and make it good writing-wise.
Luffy unlocked it because of an emotional moment.
Sanji had multiple moments where this could have been used, the best opportunity imo would be at the tea party when his family was about to be executed - instead of the retarded-perfectly-stretched-and-timed Tomato Box... Considering that Sanji has strong emotions to the point where he can turn it into power...yet Oda didn't make him unlock it.
Yes, Sanji hated his family, but he stil couldn't let them die, especialy since he cared about Reiju and that was apparently not enough of a tricker to unlock CoC. Which i find really weird, considering Luffy unlocked it to save some random girls he just met a few hours ago...and not for Vivi when she was almost ate by a Bananadile, but i guess it was too early or Oda didn't think it through at that time, but whatever.
So an emotional ''unlock'' would seem almost weird if it would happen, because Sanji had a really good moment to unlock it - it was a do or die situation, he has a really close bond with Reiju and it would have showed Judge that Sanji is the one worthy of being a King and not him, so more than enough reason to unlock it. But it didn't happen. So what kind of a situation does Sanji need to be, that would out weigh all of that for him to unlock it? Just to save Nami? Yes, Sanji cares about her, but i don't see him carrying about Nami soooooo much more than about his own sister.
So i don't think Oda is gonna go the ''Luffy route'' for Sanji, but probably the ''Zoro route'' - which is unlocking it through an outside influence.
Zoro got it through Enma basicaly pulling it out of him.
For Sanji, it could maybe be DR, in which it would also unlock his CoC after transforming.
Or the Germa thing. Sanji's loses his emotions and has to ''conquer'' his emotions to get them back or something like that.
But i am not sure how that's gonna play out, since it looks alot like Sanji is already heading to Sommer. Will see.