How do I come in as a young adult and not piss off these tenants but get them to pay or leave without destroying the property?

You can only evaluate the adults againsts your screening criteria.

My elderly tenant passed away in January.Her adult daughter continued to pay the rent till September on her deceased mother’s behalf to continue to have access to the house and her mom’s belongings.

Just decide if you are ok with pets and if you are decide what sort of pet fee (not deposit) you are going to charge.6 (or more) puppies are not house broken and tend to have 6 times the accidents (carpet and subfloor) as a housebroken adult dog.

The seller's adult children were there also and were being extremely insulting to me.

I was hoping to find a reasonable young adult for the master suit with no kitchen, I could possibly add a small kitchenette with very basic set up I suppose to make it more appealing.

Given the proximity to SDSU I thought I would get college students, but in actuality all the units are working young-ish adults.

It's a SFH 3bd/1ba with finished basement. 2 adults and 5 kids live there.

@Colleen F.Thanks for asking for clarification, because I should have said 6 adults, instead of 6 people. 

I think I just chose the wrong Sect.8 tenant: she beats the hell out of the unit, had an adult son living there who caused a bunch of problems around the building, had a dog when she wasn't supposed to, on and on.