@Natalie VaneThe outside condensing system and the inside air handler system have to run off of the same freon because they interconnect.  

"CelLink was originally founded with the goal of developing a new type of interconnect for solar panels.

There are also many more interconnections than a traditional system leading to a higher failure rate.

As for the age of the population and its interconnections to deflation/inflation, I believe that demographers estimated that the U.S. transitioned into a "primarily old" population sometime around 2015-2020 for the first time in the country's history. 

On the smoke/CO detectors we avoided the expen$e of an electrician (& permits) hard wiring them by using an alarm that features wire-free interconnectivity. 

Obviously location is everything, and this is in the boonies, not downtown NYC, but it does have some tourist draw...It's in a small rural town that is also pretty close to several other small rural towns that are fairly interconnected as far as people going back and forth.

@Eric Peterson there are multiple safe harbors and they aren't interconnected.

You've got a slew of interconnected but distinct issues to deal with...The simple answer is no he has no right to come on the property simply by virtue of being married.

A few minor fixes like having interconnected fire alarms and an additional heating source would make it 100% legal if you plan to close off the wall to make it an actually ADU.

I suggest follks stay clear of messy interconnected situations, and the worst issue(s);  assumptions and expecations within family members...Stay clean and clear of these things.