@Donna1017 As soon as you saw a pack of 18 year olds arrive with no adults, that was the moment to go over and boot them all out. It's not "okay", even if nothing gets damaged. What's the point of having cameras if you're not going to do anything when you clearly see that the guests are breaking rules?
You should report this user's account to Airbnb, telling them they scammed you, and then caused damage they won't pony up for.
I hope the communication you've been having with these people has been on the Airbnb messaging system so you have proof, rather than phone calls or texts.