There is a great way to create a new listing for all the rooms, and link it to the single rooms so a guest can easily search for accommodations for 6 people and book your place. We have a listing call 2 Big rooms in House in the Country. And we selected instant booking. It's been very popular. You could even have another listing for just 2 rooms. When someone books a single room, the associated linked listing also gets "blocked by linked listing" exactly what it reports on your host calendar.
Also, you may indicate how many beds are in each room and even add air mattress to the list.
Sounds like your place with 3 rooms could sleep 8 or 10? 2 per room plus extras?
Call and ask Airbnb for help on linked listings if you need to. They are here to help.