I have the same question and I added the name of my second guest via Hilton.com
The booking still officially shows 1 adult, even though the bed can accommodate 2 adults. I raised this was [MENTION=3648]hilton[/MENTION]Honors on Twitter a few times and even offered to pay a second person fee if it existed and they said it was fine. Not sure if we'll be receiving two guests' breakfast F&B credits during our stay next week (USA).