Looking to possibly install a scale blaster device on the main water line to see if that will solve the water issues on all three units then I can avoid delivering salt every 3 to 4 months to the other two units.

Some days they might not need an assistive device to ambulate but other days they may need a walker or even a wheelchair.

You CAN spend even more money and get battery backup with this mode... so if the power goes out you can have a small amount of energy to run things other than the HVAC or stove... like a medical device.

I have one door and my primary residence that I rent out the upstairs.In my rental over the last year I have had the following issues/calls:In the first week (when I think you will get the most calls from tenants):Toilet seat was wobbly (It was-very easy fix)Toilet seat wasn't flushing (plastic trip device broke. $10 fix)After that I had 2 calls over the course of the year:The AC unit wasn't draining properly and was leaking out into the house.

install decent exhaust/air moving devices. 

I would hold off on assuming you have a bigger problem until checking the box personally, and I would get a “tic tester” ($19.99 device that looks like a pen and tests for electrical current) and check your outlets and heater for power if that doesn’t work. 

Only 1 gas device in the building besides water heaters.assessed for 300.

On the dog situation I have no rights unfortunately since it’s an ADA animal and it’s seen as a medical device.

I suggest owners insist on tenants using surge protectors plugged in to protect their appliances and devices as well as the property in case this ever happens. 

Some need to start with sips from a good book with all devices off.