@Allison75
I think others have told you adequately that what you propose doing is out of line, not correct and will gain you absolutely no sympathy here on this forum.
If you do cancel those three confirmed bookings then Airbnb will block your calendar for the duration of those three bookings but will not have an effect on other days, but they will also penalise you in other ways.
https://www.airbnb.ca/help/article/990/i-m-a-host--what-penalties-apply-if-i-need-to-cancel-a-reserv...
I once had to turn away a month long booking because I had a 1 night existing reservation that fell in the same date range. You do not dump guests to chase a more lucrative offer!
Your most polite, ethical and courteous way around this if you feel you must pursue this is, contact each of your confirmed bookings and explain your situation and work with Airbnb to find a solution which each existing reservation will be comfortable with. Now I know this takes time and will certainly fall outside the time contraints of this booking you have hovering in the wings!
You can also message the potential long term guest and explain that you are not free to accept a booking at this time but will make all attempts to find a way of making the booking available to them with Airbnb.
This is the correct way you should go about this situation. You should never just hang a confirmed booking out to dry and cancel!! That Allison is just bad form and won't win you any sympathy from any corner.
Airbnb are good to deal with and if you and both your confirmed resevations approach them I am sure something can be worked out.
The secret here Allison is .......communication!
Cheers.....Rob