I know some places don't allow short term rentals. With that said, can you freeze your hosting, host the 6 more guests and tell your apartment they are family coming to town? That way you get paid without a fee, the guests get to take their trip and maybe you can slip these last ones by? At the same time, if it is a matter of losing your lease or renting out the apartment a few more times, then certainly keeping your apartment is most important.