Our soil is largely made of clay and our temperatures while mostly moderate have extreme cold and heat within shorter periods of time. 

But, no penalty.Pick up a couple of these and see what the actual temps are during the cooling cycles:https://www.amazon.com/Elitech-RC-5-Temperature-Reusable-Rec...Keep in mind, NO AC can cool more than about 20 degrees below ambient.

Our state guidelines say we must maintain a temperature of 65 degrees.

If they cannot produce a receipt for the hotel, I would give them each $50 or $75 off next months rent.I just looked at the temperature for your area, the tenants have a legitimate complaint.

The temperatures you have the house at are completely unacceptable.

It depends on the OAT (Outdoor Air Temperature).

It's recommended to keep insulin at cooler temperatures, but it doesn't "go bad" over a short period of time not being refrigerated.For example, although I keep insulin I'm not using in the refrigerator, the vials and pens that I'm actually using aren't kept in the refrigerator. 

I would hate to have this result in requiring AC units that tenants won't use because they pay electric blocking the window and pushing the temperature over the limit.

They assumed a family of 4 in the local area where incoming water temperatures varied significantly by season.  

We had a similar mishap a few years back due to a rapid drop in temperature on a vacant property.Where exactly in Atlanta is your property located?