Avoiding conflicts

I have already built a website for a client, for a ski chalet. There are two floors that can be rented separately, or the whole chalet can be rented as one unit. I created (last year) two calendars (using another Calendar System) – one for each floor and added a note / form for the user to call if they wanted to rent the whole chalet.

My client would actually like to have a third option active as a calendar, for the whole chalet. What I can’t seem to wrap my head around is how we can avoid conflicts. For example, someone has already rented the upper floor for say August 13-19. Now someone else wants to rent the ENTIRE chalet during the same time period. How can we do this without a conflict? Will your plugin accomplish this?