Hi @Sabine637
We have the same issue. 3 rooms and 4 listings: for complete space (3 rooms), 2 rooms, and 2 listings for single rooms.
And I've also discovered that Airbnb links their calendar one way, not the other. And yes, it shouldn't be too hard, but not apparently a priority.
We ended up un-listing one of the rooms so that we now have lesser chances for double booking (though its still technically there with one room).