Immediately send a message to the booking guest and require that the reservation be updated with the appropriate number of guest and the full names of all guests. That assumes you can accommodate the 5 guests. If you have extra fees for additional guests, the updated reservation will also be updated in terms of payment.
Be sure to emphasize that you need to have this completed or that guests will not be allowed to enter the space. Be sure you or your representative are present to confirm the number and identity of guests. Be sure to have communication via the Air BNB message system. Good luck!!