As to who's going and who's staying:
I know Heron told his watcher to wake him if Sammy called for him, which implies that she needs to stay at the theater. Sam wasn't part of that conversation, though.
And I personally don't know if it's possible to change the who the watcher is watching, esp. since Heron only got the one service.
And I'll understand if Fionn can't get the information Sam wants, given his stun status...it'll make things a bit more of a challenge, of course, but that's normal around here.