Airbnb Hostel in our house

I live in an apartment block in a now very hip part of Berlin. On the ground floor a family of four used to live in the apartment. They were pressurised by their landlord to move out because he wanted to sell the property. The new owners claimed they would move in themselves. Instead they installed twelve beds in four rooms and have converted the apartment into a hostel which they list on Airbnb. That’s twelve people staying in a apartment meant for a family of four to five people with guests changing every three to four days. Our children can no longer play in the courtyard unsupervised and our privacy has been violated.
Of course, the hosts of this hostel never asked the residents in the apartment if they were ok with any of this,and they deny what they are doing. This leaves us to have to prove to the authorities that there is a hostel being run in oue house which is taking up time we would rather spend doing other things.