What does your state/county say about hability standards and temperature because a nest thermostat may help you all pay utilities if they are in your name, don't go below or under the legal limit and don't risk your pipes. 

Dear Airbnb people, today's crazy idea would be to live in 3 different cities year-round, trying to keep the wife happy with 75°  the day's high temperature.

You could also have a separate agreement outlining house rules...I havent done this but it's something i'm considering.Here are a few issues that have come up while I've house hacked:- Tenants disagreeing about how clean the common areas should be, WHO is cleaning, and whether it's worth having a cleaning service (monthly)- the house's temperature- Some tenants leaving things out in the common areas and other tenants getting annoyed at it.Every situation is going to be different, but if you've ever lived with roommates...it's similar to that, except you're not paying rent! 

We let the water run for a bit, I went outside to the water heater and turned up the temperature to “very hot”.

Also, I don't know what the problem is with heating and cooling in most hotels but I find I can control temperature much more easily in Airbnbs.I suspect that nightly rates for many urban Airbnbs have risen as regulations have reduced competition.

One of the primary benefits of mini-splits is their energy efficiency; by enabling individualized temperature control for different zones within the house, they significantly reduce energy waste associated with heating or cooling unoccupied spaces.However, a common concern with this approach is ensuring that areas not directly served by an air handler, such as hallways and bathrooms, also receive adequate conditioned air.

I think step one is throw the option on the table and get a temperature reading if it's even a possibility.

Currently they are complaining that the refrigerator temperature is hard to micromanage and that the freezer door seal is a little "leaky".

The temperatures have been unusually low and pipes in the home froze for 5 days so far, making the house unusable as a short term rental. 

Try putting in honeywell 9000 thermostats in-between guests.You can lock in a temperature range they have to stay in.Have your system serviced if it hasn't been in the last 12 months.You don't want the guest to put utilities in their name for 90 days.