The 2 older adults would be the market.  

I've had qualified renters move into a rental, add their bum friends or family members, and then disappear, leaving me with bad renters who weren't approved and aren't on the lease.The best practice is to screen every adult, approve them, and add them to the lease. 

Does anyone have a template or method that they use in order to screen tenants effectively in order to reduce the risk of non payment and damage to the property? 

guests=1&adults=1&s=67&unique_share_id=6413afb1-1f4f-465e-9828-521b480103c3

guests=1&adults=1&s=67&unique_share_id=1ad32050-c8a3-4f7e-95e9-ce2c43297af8

For example, I mention that every adult must pay a $30 application fee, pass my credit/criminal background, make a combined income of 3x the rent, and whether or not the property accepts pets.

And they execute their investment strategy/model (develop, resell, hold, etc.) effectively to generate a return and/or equity and make a living.

When you have multiple responsible adults sharing a house, if one "bad egg" slips in then you have the others renters to kick them out or report them. 

It has nothing to do with marital status or one's relationship with other adults.

I am a little late to the game and have been told several times throughout my adult life to invest in real estate, but I ignored the advice.