But no matter where you use the down payment money from, any bank is going to want to know where you got the money, so just be sure to be honest and disclose that info to them.  

I have a few suggestions for you, don't know exactly what your credit situation is and I'm not asking you to disclose everything here.

More sleuthing disclosed that the magic number is 75%:  When a builder or renovator sells a house where he has rebuild or modified 75% or more of the footprint / ft2, then he has to provide a New Home Warranty to buyer.

Off market usually involves wholesaling in some flavor, or another where an investor puts a property under contract and assigns it to another for about a 5-7k profit, or dual closing where the wholesaler is closing on a purchase, and immediately selling it to another investor - the purpose being to make maximum profit without disclosing profit made.Realtors can help you with both options, but primarily the ones listed on MLS.  

Realtors in most states are required to disclose any material facts that they know about the condition of the home.  

What we email has about 95% of the information that is in the MLS, however there is certaino information in it that is absolutely private that can not be disclosed to laymen.

Keep in mind though that if they have the house under contract, any new easement would need to be disclosed to the new buyer and the neighbor may not want to possibly interfere with his sale.

I have wholesaled real estate in the past and have always disclosed this to the seller especially in writing. 

Not sure what the paperwork you signed for at closing disclosed about the lease they currently have, I would look at the lease see if it has a clause for change of ownership and see how the terms may carry over or end.This way if you end up in court all your paperwork has you listed as landlord and it's not confusing for anyone.

In other words, if the buyer finds out later that there's a non-disclosed lien on the title, hidden termite damage, or some other unknown defect that would make closing impossible or inadvisable, they are SOL, as the saying goes.