So basically I have a game with a hub and a few places to teleport to via ReserveServer.
Sometimes in the server a random number of players will be teleported into the server and I want it to wait until everyone that was teleported is in the game before going on to it's functions. How could I tell that server how many people are joining or is there a way I could do this?

2 comments
You could have a 'party leader' who is teleported beforehand. But before he/she's teleported, you save to their datastore the UserIDs of all of the players in his/her party. From there, you just wait until each of those players has been added to the server. Never tried this before, but seems like a reasonable theory at least :P
Ah, and when he's teleported into the server, do a quick check to see if the other players are already present; it's possible that they would connect faster than the leader does.