How do I set up the documents to do this? 

Have materials documenting the financials of the property they're staying in and every other property you've done behind that in a binder.

There’s your documentation, not including the mortgage company’s documentation showing dad’s mortgage payments and then hers. 

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

Nor will a title company provide a complete loan package.Your friend needs a lending attorney to prepare a set of loan documents.

Lenders that do DSCR loans for foreign investors typically require bank documents to be translated and currency to be converted U.S. dollars. 

Be sure your attorney drafts the documents for your protection . 

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

Of course, the rate can be slightly steeper than the conventional loans where it is a full document loan, where they need to qualify you based on your income.Alternative way, is to acquire the 2nd property as an investment property with conventional, while putting 15%-25% down payment.

make sure you have cash reserves. as soon as you sign, you could give them a 60 day notice of rent increases. documentation of the owners lease agreements with each tenant & rental payment history. you could sign a 6 month lease with everyone to see how things go. licensed & bonded contractors, someone who can take accountability- you can send an email too if something goes wrong (the boss).