Congrats on your progress so far.

I am familiar with the standard Zillow and alike applications.

The logical (or maybe traditional) progression is to move onto larger and larger properties, which I've had my eyes open for.

The problem is finding the Path of Progress where your property value is really going up.

Do most apartments use third parties to screen applicants?

To further clarify, the investment property will be purchased with100% cash that was obtained from the HELOC so there would be no loan applications at the time of initial purchase.  

Keep us posted on your progress, and don't be afraid to ask any questions. 

But even that site has caveats, is clearly sampling only SFRs (not reasonable in high density metro areas) and assumes a $1,000 rent which not even a national average nor applicable in many cities.If only this kind of analysis could be automated and kept up to date and be more inclusive.

I’m thinking I should have the two brother fill out applications and if they pass have all three sign new lease and not extend time.

Just keep reading, listen to the podcasts if you haven't started already(SO motivating and filled with a wealth of applicable information) thanks @Joshua Dorkin and @Brandon Turner.