HI @Dave42 the guest should have booked for 2 people so that you knew how many you were accommodating. But you are not going to get any more money because you've set up your listing so that there is no extra charge for any more than 1 person. In the image below you can see that I looked at a booking for 2 people for 1 night on 1 August and the price was the same as for 1 person and it shows extra people: no charge.
You should go to Pricing Settings -> Additiponal Procing Options and enter the amount you want to charge for extra guests after 1.