Posting a related data point.
Because you can only have exactly TWO people on the reservation if you want to use the companion certificate, I had to put traveller #3 on a separate reservation. There were no more three seats together in the peasant section that #3 (peasant no status) has access to. So I chatted an agent to put all three of us forward to the elite section (not first or premium). It was done easily and quickly.