Yes, ok then do this:
Conditional branch:Hero [x] in the party
<>Teleport to wherever you want
Else
<>Message:I shouldnt leave by myself
That's to check at the teleporter. You said you wanted it so if you said no, then you couldn't leave. That'll handle that, although I would have it check for a variable rather than if the hero is in the party. It'll cause for less problems in the future most likely.
As for the hero event, Jesse was on the right track:
<>Show Message: Hi, we love you, let us join you so we'll always be with you forever.
<>Show Choice:
<> [That's really weird, but ok] Handler
<> Switch 0001= ON
<> Change Party Members: Add Arshes
<> Change Party Members: Add Basil
<> Change Party Members: Add Gloria
<>
<> [No, get the hell away from me] Handler
<> Message:
<>
Then on the second page, make the precondition that the switch is ON, and put a blank image in for the graphic, so you remove all the members that just joined from the map, and thus, when you re-enter, the event won't repeat. If you use mark's way, then make the conditional branch check for one of the members. But of course there are other ways, you could have it check for the switch or even a variable for example.