@Rhonda45 Rather than just asking the guest how many are coming, tell them that as they mentioned "we" yet only booked for one, that any guests above 1 won't be admitted to the property, and that they need to enter the correct guest count for the number of people who will be staying.
You have to make it sound like not answering will result in a bad situation for them.
And put that info in your listing and as well, that only the guests on the booking will be admitted to the property, and that arriving with, or having extra guests will void their booking.