While they are all individual reservations they can be "tagged" together and you actually see the grand total on your last invoice. The next cruise agents on board like to do this and it creates nothing but issues later on for travel agents if they want to move bookings into a group or even getting "clean" invoices for each reservation.
I would tend to say that it was a Concierge who came from a non Oasis class ship and just started using the letter they had in their file or a new letter was sent out by corporate for all ships without the one specific to OA class.
At this point just have them be a no show. They will get taxes and fees refunded for the 2 no shows post cruise.
Also, by doing the above they still leave options open should something change.
Any other family or friends not going. Name changes are allowed up until 48 hours prior to sailing
I was on Oasis with a partial charter of over 500 people and other than seeing the same t shirts we never would have known they were on board, it never affected our cruise.
There are many rules that they must follow based on where the homeport.
Drinking age for North American sailings
VAT charge on certain European itineraries
gratuities included for Australia and Casinos for Australia are just some.