No, it doesn't work that way. Usually the TTE obliges when one pax shows the ticket and says the remaining will board elsewhere. But he is well within his right to allot seats if he finds no passengers there. He is just sticking to the rule book mate although most TTE often show a bit of consideration.
The rule says that ONLY ONE person of the entire group has to show the tickets and not everyone. The rule also says that ALL PERSONS are required to board at their designated boarding stations failing which the TTE can allot the seat to someone else. You have just mixed up both the rules.