(We're aware of the five year look back period for Medicaid eligibilty but it's not a big factor in our decision to do this.)We would get the house appraised so we can document paying FMV.House would be purchased with cash (it's a small home in a rural area and value is low)Inlaws would sign a lease so that it becomes a legitimate rental and we can deduct expenses, etc.

Is it even possible to do or would they have to sign a whole new document?

When we reached out we were told that the deeds had not been transferred and we owed them some notarized documents.

If your market isn't as hot right now or if you don't have significant equity in the home, then chances are you may be better off submitting a contingent offer and relying on the market. 

However, I do know septic inspections and repairs are more documented and regulated. 

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

Contracts, financials, and supporting documents are the backbone of the process, and missing even one can lead to delays or worse.Third-party inspections—like surveys, appraisals, and engineering reports are also key.

Not just in the setup, initially, but separate bank accounts and properly signing all documents as a member of the LLC, even if you post on your personal social media accounts about a property owned by the LLC, if someone sues you, they will try to use all of that to get to you personally.  

, my ID and documentation that shows that I am the owner of the property such as a closing statement.I called again this morning, Monday, only to be transferred to voicemail, so it looks like customer service for when your account is locked in non existent.

Of course, with all things, the situation varies and no one on these forums has seen your underlying documents and the actual terms, and thus, you should consult with legal counsel specific to your situation.