First thing is that you live in a huge country with millions of people, so whatever you choose to do, there are people out there who will be happy to book with you, and people who won't. So in the grand scheme of things, you can still get bookings and earn money.
Second .... at the moment, your room 2 has a private bathroom. The minute you change that to "shared" bathroom, you are devaluing that room. Will the extra income from a 3rd room, also with "shared" bathroom, compensate for any lower fees due to sharing a bathroom?
Put yourself in the position of a guest. Would you want to share a bathroom with someone you don't know? What if you're desperate for the toilet but the other guest is happily reading a book while he does his business? And what if the guest walks out saying "I'd give it 10 minutes"? Or what if the other guests are a young couple having a bit of fun in the shower? As a guest, would you be ok with that?
If it was my house, then my first preference would be to see if I can remodel the layout to get a small bathroom with shower for the 3rd room. If not, I might add the 3rd room to the 2nd to make a 2 room rental with private bathroom. Instead of attracting only couples, you could be attracting small families (parents + child) (or maybe single parent + child).
Something you could do to "test the water" is create a new listing on AirBnB for the 2 room rental, leaving the original room 2 listing unchanged, and link the calendars - a booking on one will block out the other listing, so avoiding double bookings - you could get some bookings for room 2 only and some for rooms 2 and 3 together ....
Please let us know what you do and how it works out for you!
