Flying EWR-ATH in J on a booking with 3 others. Would like to upgrade to F with miles, will most likely have to be at the check in counter due to availability.
Say there are only 2 seats in F left once we arrive at check in and 2 of us on the booking want to upgrade with our miles, while the other 2 will stay in J.
Will us all being on one booking be an issue? Should I preemptively split us all onto separate PNRs? I don't want that to be what stands between me being in F and 777 J

Especially with a clueless contract check in agent.