Yes, you'd make two individual listings, and one that combines them for a 6-person stay. Be sure to synch the calendars so the reservation of either individual listing will block the calendar on the combined, and visa-versa.
https://www.airbnb.com/help/article/289/how-do-i-list-multiple-rooms
I don't think there's an easy way to copy an entire listing, and folks will only see your other listings if they click on your profile. But you can mention the other listings in the description (and possibly link to them?)