I don't know. we have three adults (my parents and I) and 1 infants, I called the hotel directly,they said no way to put the extra person even I pay extra, so I decided to get another room since the hotel in London or paris is very popular during the summer. I am afraid there is no extra room avilalbe and they don't allow us staying in the same room, then we will stuck.
Actually at first I booked one room in Paris, and tried to book another room in the same hotel later, and they sold out. So I have to find another much more expensive hotel to get 4 person settled. Luckily I can cancel the first one without charge. BTW, I booked the hotel at booking.com.
Good luck with your hotel search.