I assume your Borrowers are individuals who lived in the property and owner occupants generally pay a lower interest rate. 

When analysing an Airbnb property how can I confirm the owners claims of past occupancy? 

I started by looking at typical vacation destinations (popular beach/mountain towns), but after researching occupancy rates on AirDNA, I was surprised to see that occupancy rates in my hometown area (an ordinary suburb of Dallas) are just as high or higher than those in many major tourist areas.

I closed a smaller apartment deal (1998 build $70,000 median HHI area solid property condition 100% occupancy rents $100 below current market with no fix up located in a growth market - rated #1 emerging MF market for 2022) a few weeks ago and I used a 6% exit cap for a five year hold.

Not sure what the short-term rental market is like in CT Beach areas, in terms of cash flow, regulation, saturation, occupancy /off season opportunities etc.

It might be worth offering the tenant $5-$10k to move out with 30-60 days notice so you can sell to an owner occupant.

But the real way is to take the GPR, which is full occupancy at market rates, and then apply a vacancy factor.An easier way to think about it is: items that should NOT be in NOI.  

And what is your occupancy rate?

Unless you have four completely separate water lines, 4 hot water heaters, etc. then your best bet for sub billing is splitting based based on unit sizes or number of occupants.

Based on airdna numbers using the rentalizer here are stats for the house you provided above 3/2 based on 6 person occupancy.