You can have the "I'll grind it out/sacrifice now, so I can live great when I'm 60" mentality only for so long.

As Sue suggests, I would prorate the rent for next month a bit, and then put a mental note that this tenant will be out the first opportunity you get, whether it's a late rent or lease up. 

The third bedroom (the smallest) was going to be occupied by the mentally challenged teenager, and the two remaining children who "could watch over him". 

(who is not a licensed mental health professional) that her young son has attention deficit disorder and a service animal would mitigate the symptoms he is experiencing. 

Landlords that do not quickly adopt this mentality are targets for the vast number of professional tenants in Ontario.

Don't mentally kill/write off this deal because then it will be gone. 

:  My parents are the traditional "Poor Dad" mentality and I would like to make this mutually beneficial for both them and I.  

On the other hand, you definitely have to consider what other investors are thinking and what their mentality is about buying and how much the 70% rule is ingrained in us.

People tend to get mentally lazy when they use someone else’s spreadsheets and not understand the logic.  

That mentality is baked into the culture in both Flint and Detroit in so many places it's not funny.So, if your population can't read, has no idea what professional behavior looks like, and has a cultural aversion to working harder than the other guy (lest you take his job) you aren't left with much.