Hi Jed,
That's an easy one to answer. Our customer services representative will only have checked the main tour where there are 12 travellers booked. The "missing" travellers are those booked on the main tour with Amazon add-on.
I've just double checked these are there are now 12 on the main tour and 10 on the add-on so there will be 22 travellers in total on this tour.
Kindest regards,
Julia