Interesting development in this story.
So as I mentioned, they arrived when I wasn't home, and when I did make it home later, they had left and gone out. So I hadn't ever met them in person.
This morning, I get up early, planning on meeting a friend, and when I go out the main part of the house, I discover four people sleeping in my living room.
I left the house to make my appointment, but I sent a message to the guest who booked the rooms and asked, simply "How many people are in your group?"
About 20 minutes later, I got a response, "There are ten of us."
That was the last straw for me. I called Airbnb and talked to a rep who looked at the message history (And responded with, "Oh my gosh! Ten people?" when he read her message) and asked how I wanted to resolve the situation. I told him I'd had some other issues with them since their arrival, and I was no longer comfortable with them in my house.
So the rep called the guest, then called me back to tell me that he had explained to the guest that she had violated the house rule and airbnb policy and that she and her group would need to leave as soon as possible. He told me she took the news quite well and agreed to leave.
I had a friend run over to my house to make sure they left without incident.
I just got home a few minutes ago. The house and rooms are actually very clean. They did a great job of picking up all their messes. The guest left a long note in my guestbook saying basically that I have a very nice home and they wished they could finish out their stay and that I had ruined their trip and they didn't know they could only have six people and I didn't make it very clear about the maximum number of people.
I'm guessing I'm not going to get paid for the nights they didn't stay. The change was made by the Airbnb rep and showed up as an alteration to the booking, not a cancellation.
So now I get to compose a review for this group...