You call #TeleportTarget as soon as level starts, so there are no other clients on the map at that moment. If you want to teleport the overall Heroes party on some event, write a script, which will contain event-handling. For example, if you want to teleport the party when somebody switches a lever, write a script, which would check lever state and call #TeleportTarget routine when the lever state changes.
Duty is everything, the greatest of joys, the deepest of sorrows.