Other than that it's only two small entrances and cleaning the cars off, almost no walkways or extra driveway space.I'm under the impression (at least in MA) that I can't (or it isn't illegal) for me to dump snow removal on the tenants.

There is an outside entrance and a locking door between the laundry room and the lower living area.I have already discussed it with the tenant and have a verbal agreement that it will be shared but want to put something in the lease.

Is the exterior Stucco.. mice love stucco they crawl right up the walls..Trim back tree branches, and check exterior for cracks, and holes near basement windows and entrances. also around ac units.. 

After considering my problem more I believe I won't have a water intrusion problem since the entrance and back part of the crawl is already accessible just not with a full 16 inches of clearance and it's always stayed dry.

Then an entrance that could be jazzed up with some planters or something, because it also looks bare...

One issue I don't love about the current setup: one electrical service entrance/meter and the current owner (bank) pays all utilities for both tenants.

I am thinking of hiring a contractor to replace the window of the Airbnb room with a sliding door, giving guests a private entrance.

Can I build a house that has a granny flat and side entrance and rent it to two different people and still consider it a single family home?

Either way you need to get rid of the colony and their entrance.

The bigger unit has 3 bedrooms and 2 baths with a separate entrance.