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

Your loan document should say.

What documentation will I need to provide to the IRS in the event there are any audits? 

As with any Real Estate purchase, you need to read the documents carefully.

I have documentation that’s states she gave $850.00 on escrow statement.

Oddly enough in this document they define multi-family as: “ "MULTI-FAMILY" means a structure containing three or more dwelling units or a bed and breakfast dwelling that has six or more guest rooms. 

Just because a plaintiff files a subpoena doesn’t mean that the documents requested have to be provided, a subpoena can be “fought”.  

It's also about your ability to access the Sponsor's financial and managerial documents on the go so you can control and check what is happening regularly.

If there are large deposits the underwriter will ask for a signed letter of explanation from the borrower along with supporting documents.

So when I have someone coming from, say most recent was Brazil, I ask for supporting documentation from his home country.