Well, look at what makes sense, when you frame the scene. For social conflicts, it just doesn't make sense for everyone talking at once. Instead, you choose one person who is best equipped for the job and let him do it. If he can't get it done, none of the characters will. I wouldn't just let another character try afterwards, if the first one fails, that would be ridiculous. They are all talking over each other, each with a different strategy and each with different knowledge. It just won't work.
And quickly back to framing the scene. If you think that Marcone wouldn't be flustered by some newcomers like that, and I think I might agree there, then that is not an option. Look at it as social immunity, though it doesn't have to be a power, really, it just comes from what is true in the game world. But the player go up against him for a reason. They need something from him, or they want him to back of on something, or whatever it might be. Talk as a group, what would be a reasonable thing for Marcone to give up, and what the players might have to do in return. And then have that be the stakes the social conflict is playing for.
That way, they can't run the big kingpin out of town with one lucky roll.
