@Chris14748 You can request to alter the reservation to include the extra adults. The guests have to approve it so just send them a message letting them know the request to alter is coming and that they are required to approve. If you have extra fees for extra people it will automatically be applied.
The slightly tricky part is if your listing doesn't currently allow five people.
You will have to go into your listing first and make that change to five people, then create the request to alter reservation. You can change the number of allowed people back and it will not affect your reservation.
If this booking works out well for you, maybe you would like to invest in a small cot for such situations.