Can either do it as a 2nd home, will go off DTI & many more documents. but that’s the right idea, cashout refinance and use the proceeds to payoff the other heir.

All documents are recorded.  

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

I documented everything but it doesn't matter because once an eviction is filed, rightly or wrongly there are companies collecting this information for databases for future landlords who won't be bothered to consider the facts. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Here is the city's page that outlines the RTLO, and has a link to the complete document: https://www.chicago.gov/city/en/depts/doh/provdrs/landlords/svcs/residential-landlord-and-tenant-ordinance.html. 

Yes when going for a personal full doc it will require all of that documentation .

It would be the underwriter that just needs to document the 6 month seasoning before closing in order to stay within the terms of Fannie/Freddie guidelines. 

Did they give you a roadmap or strategy document to follow? 

https://www.biggerpockets.com/blog/what-documents-do-you-nee...