I am a little bit confused. Your advertisement is for the entire appartment correct?
which consists of 2 bedrooms.
Which means it is expected for the guests to be able to use the entire appartment. which you have also noted in your advertisement.
so the way I see it you should always expect that all rooms will be used and should provide a cleaning fee accordingly.
Even if only 1 person were to end up booking your room, that person could still decide to sleep in 1 room the one night and in the other the next if he or she wanted to. Aterall they booked the entire appartment and are able to use it.
and especially if there are 2 guests or more.