Should a Muslim's companion return the greeting to a third party?

Initiating the greeting of peace (Salaam) is a Sunnah and a cause for love among Muslims. Initiating it is a Sunnah, while returning it is an obligation. The Sunnah is for the younger to greet the older, the passerby to greet the seated, and the few to greet the many. If this order is violated, and the greeting comes from the other party, it is still sufficient and fulfills the Sunnah, but the former is more complete. It is obligatory for the one greeted to return the Salaam. If the one greeted is a single person, it is an individual obligation (fard ayn) upon him. If they are a group, it is a communal obligation (fard kifayah) upon them. If one of them returns the greeting, it suffices, but if all of them return it, it is better. If a person greets a specific individual, others are not obligated to respond. However, if they greet a group generally, then one person from that group responding is sufficient.