messaging Delta yields the answer that says the record/reservation will take the status level of the primary passenger (in my example, then it would be seen as a GM level priority).
calling Delta yields the answer that says 'no matter the order of people on the booking, if there's 2 and only 2, it will be seen at the priority level for upgrades on the highest status of either passenger'.
So - there it is. I've done a booking as exampled above - GM logged in, GM was 'passenger 1', GM added passenger 2 who is PM and in a few weeks we'll see if there's decent upgrade priority or not.
