Worse, what happens now is everything you’ve been submitting is too old to use.

if not, you need to change your PA's too : ) Did the tenant provide any proof they submitted a WO? 

If the sale was by a quit claim deed, or almost any other deed other than warranty deed, then depending on if any other documents were signed by seller regarding liability for “back taxes” he may not be responsible.Since as to the taxing authority the taxes stay with the property, if you or someone doesn’t pay them, and assuming no mistake was made as to their status, then your property is subject to any and all relief available to the taxing authority, including lawsuit, lien, or foreclosure action.

The value of the contract at closing is to be $45,000 as outlined in the attached agreement.This document is a separate agreement between the seller and Anthony Michael Minutoli-ME (the buyer).

I also requested additional documents like estoppel certificate, mold remediation that the seller isn’t able to produce.

You may need to file documents with the city to let them know it isn't a primary residence (tax purposes) and they may require rental registration and/or inspections. 

Biggest advise is document, document, document.

One document we used was an appeal letter to the IRS saying that all proceeds from the sale would go towards the lien.

What other documents would we need in order to protect our lenders and ourselves?

Document the purpose of every expense.