I'm with other posters - this is a pretty silly move, but that's my opinion.Your original question was "Is it possible to buy 3rd, 4th+ primary residences with 5% down" per the thread title.The answer some folks have given is that if you do this, it could be interpreted as mortgage fraud under the current rules/guidelines from CMHC about what they're willing to insure.

He later got kinda rude/(I kinda interpret it as him trying to be manipulative) and said that if I let him move in that he would be willing to overlook the fact that I had turned him down in the first place. 

Unfortunately the city has a different interpretation and allow ADUs strictly for SFRs.

And any oral agreement can be misquoted and interpreted in an infinite number of ways.

I've heard of this happening from one of my lawyers - who wants everything "clean" - so no judge can interpret things any other way.  

Judges here are voted into office and have a much more consistent interpretation about protected classes than whatever dream tangent you have built here.  

Do you want someone who isn't qualified to the same standard interpreting your MRI or doing trauma surgery on your sister who got into a car wreck?

Now I’ll spread your fame, that’s one of the wisest interpretations I’ve heard

Blah, blah, blah.The term "reasonable" is up for interpretation but will typically be clear to a casual observer, and certainly to a judge.

My client couldn't speak English and had to use an interpreter to close the transaction.