The issue is, after asking them, my neighbor/tenants will not update their mailing address to include the "1/2", so I am regularly getting their mail and placing it in their mailbox.

I have been investing in Milwaukee since before it started trending 10 years ago and never had an issue with rental demand. 

I have State farms on my main house & attached ADU, but since they are NOT issuing new policies in California, I have been unable to find an INS company willing to just provide INS for my rental.

Actually he brought the issue to your attention, was absolutely correct and the best thing you can do is make a note of it for the future. 

Common culprits include poorly sealed wax rings, dry traps from leaks or non use, and localized clogs that vent sewer back into the room. 

Make sure there will be no issues renting the home.

If they have other property (outside of a primary residence) then it could work out but you have zero equity protection and going in 2nd behind hard money provides all sorts of risks and issues, even if they allowed you to.

For example, what happens if you identify a property and then cannot close on it due to inspection issues or other related problems?

That worked best and we never had issues with rentals or any negative feedback.

Our experience underscored the reality that, in a nation where renters abound and multigenerational living is increasingly common, the challenge of overcoming prejudice and exclusion remains paramount.