So what is the plan with A actually? Go blindly into a complex large enough to hold about a thousand people and try to sneak into the prison that we have no idea where it is? Or just sneak around trying to find some evidence or clue that we don't even know exists, let alone how it looks like? Come on, there is a reason thieves case the target before breaking in. We could be stumbling around all night and not find what we are looking for. We need information before going there - at the very least a layout of the place and the location of where they are holding prisoners.
Now we've hit the crux of the choice here and it has nothing to do with which attributes we trust, though our CHA/Speech and AGI/Stealth are both quite good. If things were just as simple as picking which skills we're best at, this whole situation would be a lot easier. The trade-off between A and B is this: A involves going in blind and without a plan, while B involves going in with a massive liability in Yifeng (i.e. a plan, just not a very good one). So why would I pick A over B? Because I just don't see her being able to hold up our cover story. Based on that, relying on ourselves seems to be a much better bet than relying on someone who we need for a task that they're not suited for.
You also haven't come up with any reason why they would allow us to speak to Yao to begin with. The logic of "I don't see why they
wouldn't let us talk to him" isn't very convincing when you haven't really described why they
would. This girl apparently lost her father to Yao, why would she let some stranger with close ties to him talk to him?
Given that we will be negotiating, not Yifeng, I will vote B. Why? Simple, Speech 5 > Sneak 3.
We should be very careful with that logic. While playing to our strengths makes sense, things are never as simple as applying our best skills to every situation that we come across. Context matters a lot: we have an Unarmed skill of 5 and great physical stats, but we know it's not wise to pick fights with guys like Zhang simply because that's what we happen to be good at, because we'll get our asses kicked. Similarly, our silver tongue isn't going to be of any use if we have Yifeng's naivete undermining us.
This is why sneaking into the place will prove to be a more beneficial way of getting information - we don't have to necessarily get Yao or Cao'er out of there right there and then. We could sneak in, discover where they're located and talk to Yao to understand the situation from the source that we trust the most to have the full facts here. You guys are right when you say that it would be foolish to bust them both out then and there, though: we aren't going to be getting the both of them out of there.
Really, I think that the only surefire way of getting them both out is actually C. We'll probably have to give up the Yuchang Sword, but the Abbess will be grateful enough to pull some strings for us.
That's not wrong, but it could also suggest a dearth of new candidates for the Castration Squad, if the only person they can replace a vet with is an untested newbie. Nuns are old because no one ever manned up to replace them, that sorta thing.
If they have a dearth of candidates, they wouldn't have left her behind like that in the first place, no? Do the more ascetic sects like the Shaolin and the Emei have fewer members in general? I wouldn't be surprised if that were the case, given the level of dedication and sacrifice that joining them would entail.