The hero is clearly not the leader of the hero party, perfectly openly. What a weird situation. Maybe he should seriously consider accepting the leadership role because his party members, that are now in control, are overly aggressive provocateurs. It makes no sense for the hero party to actively seek trouble where there was none before they appeared.
Yes. The clown troupe. Or something like that. If I'm not recalling it entirely wrong, Rimuru even suspected Yuuki being involved somehow. Rimuru's a bloody good actor, though, not to let any of it show now that he went to meet Yuuki. Maybe he offered access to the ruins to be able to keep an eye on Yuuki's people. Too bad it also works the other way.