Oh dear. Well who knows what people get up to behind the closed doors of your property and as to people being naked inside, well it's hardly public indecency if they are not exposing themselves to others. But eight guests instead of two? No way.
This is where it become so important to be super strict about the no extra guests/visitors rule. I am a home host and, while I do have to occasionally tackle guests who think it's okay to bring extra, unauthorised people into my home. I have actually found Airbnb CS to be quite supportive on this issue. They do not approve of extra guests who are not paying because they are getting nothing out of it!
Sounds to me like security cameras (outside ones, filming entrances and fully disclosed on the listing) are in order and a very FIRM warning in the house rules that anyone who brings unauthorised guests will immediately be asked to leave.
I'm not being a prude or anything but I'm not having people shoot porn here. It could all be perfectly above board, but how does one know for sure? How do we know minors are not involved, for example?
Besides that, as someone who has often rented out my place for photo and film shoots, it takes a lot of detailed management to make sure that things will not get out of hand/damaged on any kind of shoot. Forget the porn, there's no way I would have an unauthorised shoot on my property.