AirBnB model is based on an initial price for one person, then an extra charge for another person (staying in the same room usually), plus any cleaning fee you wish to include.
Seems to me like you need to create a listing for each room - then people can book as single guests, two, three, four and up to six.
Otherwise people will never know you can accoomodate more than 2 people.
Do a search for some other properties that can accommodate more than 2 people and see how they are organised.