Plus when the landlord rented to her, it was a family of 5 which then became a family of 7 and is now a single mom with several adult children and their partner living there along with her boyfriend. 

Not to mention you're a big bad evil investor pushing out owner occupants and driving up the cost of housing by taking away homes from young adults who grew up on the internet and know how to get noticed on social media. 

I explain application fee per adult in home, income 3 x monthly rent, and must have good rental history and cedit.Most that do not qualify will either say they will call back or just let me know they do not qualify.

, no extra adults living there (like three other waifs).

They need to work through this as adults.  

I've been a renter for most of my adult life and this was the first time I wore the other hat as a landlord witnessing the tenants from a landlord perspective.  

I can't make a decision until I have a COMPLETE application from all adults who will live on the premises and be on the lease.

Call Adult Protection Social Service and report that she is in a horrible state and that you just took over the building and am concern her apartment is both a health and safety issue, next call the health department and ask to speak with the inspector about coming out and looking at this unit.

He is only 18 and boy he is discovering that 'adulting' is very hard lol so I am trying to be kind to the kid.

The roof over the adults head is the same roof that provides for the child, but what about food, clothing and items children need, but cannot get easily on their own.