Originally Posted by
Duke787
However if a 5th person is added to the list before then, the system will skip the 2 of you (because there is only one seat and there are two people on your PNR) and upgrade #5 on the list.
That's not my understanding. The "system" won't skip you and companion to upgrade #5. It'll go to the gate. The GA should call you and ask if you will split in order to take the remaining seat. The GA may not call you and start boarding, though, before upgrading the last seat. If you and companion board, they'll likely end up upgrading the 5th person assuming they haven't boarded as well.
All that aside, you are likely seen an early snapshot of the upgrade list. As more folk check-in, you are just as likely to see your name drop down the list. You won't know the true picture until you get closer to the flight time.