Airbnb has hands off policy on this matter. You are out of luck. Call the police as they are trespassing your property.
If they have stayed over 30 days, in California, they have tenancy rights. Then you are more than in legal, emotional and financial jeopardy.
situations like these brings what Ted Bundy, a serial killer said in mind, people get killed because they are polite.
stop accepting guests that seemed odd to you. Follow your intuition. There are many wonderful guests out there. Leave your listings open for those good guests and don’t worry about the bad guests. And make sure to review your guests honestly. By being polite or worse, being dishonest, you are not doing any favors to other hosts.
also I just asked Airbnb if I can read guests’ reviews of hosts. We shall see what they say.
because you can learn a lot by what guests say in their reviews.
MeehyunK