Hello @Hermine1,
When I go to your listing I see a price of €100. In the "Prices" section it says "Extra people no charge" so the €100 is for the everything, all 5 rooms. 16 people can arrive and use all 5 rooms and the total price will be €100 per night. 100/16 per person. If only 1 person arrives it's still €100.
If you want to be able to rent each room separately you have to have a separate listing for each room.
If you want to have a per person charge you can set the extra people charge to be $X after the first guest.
Many people on here have reported the "These dates are not available" problem. I haven't seen any solution to it.
You could contact Airbnb customer service.
To find ways to do that type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. A list of suggestions will appear. Click on the "Contact Airbnb: A Community Help Guide" one.
Steve.