I had this same situation when booking a domestic flight within the US with AA
There were 4 of us but only 3 O seats left and then Q fares.. Whenever I selected 4 it priced as 4xQ as we were all the same booking so I had to do one booking for 3 which gave 3xO fares and then 1xQ Fare on a separate booking otherwise because you all have to be the same code it was pricing as 4 x Q