This is a third-party booking and breaks Airbnb's terms & conditions - you'll want to get in touch with Airbnb to see what your options are. You'll also want to think about what your goal is - do you want them out? Is it okay for them to stay so long as you are paid the additional person fees?
First, I'd establish your side of the story in Airbnb messaging.
"Dear travel agent,
It's come to our attention that you aren't one of the guests staying in our listing, and that you booked this stay as a travel agent. Third party bookings are a violation of Airbnb's terms and conditions, unless made through a Airbnb business acount. In addition to this, we have security footage of 16 guests, not 13 as stated on the reservation confirmation; the additional person fees would be $xx. The occupants also tampered with security cameras, which is a violation of our house rules.
Sharing our homes requires a degree of trust in guests, which you unfortunately have violated. We will get in touch with Airbnb to see how to resolve this situation."
Then call Airbnb to see what your options are. You could push to cancel, but may have to refund (full? partial? none?). You should have a strong argument that the guests are the ones violating T&C and therefore shouldn't receive any refund.
I'd also suggest you add the following to your house rules: No unregistered guests are allowed on the property at any time.
This solves a world of issues with "oh, they just stopped by for a minute" guests who are still there at 3am. If they aren't on the registration, they shouldn't be there!