They would have to provide proof that they did the work in order to have an enforceable lien. 

You’ll need to show Proof of your ability to buy, and an EM deposit,  before they will look at a purchase contract.For wholesaling, you need to find off market, desperate and/or ignorant sellers.  

The bank did not have me sign anything saying I would sell the house, just needed proof that the house was on the MLS before the closing date.  

If we want to make an offer in the meantime, how do we show proof of funds and how soon do they expect the full payment.  

If you want a signature as proof you would have to use Docusign or maybe you could create one in google forms.

If I am looking to sell any of the buildings I have proof of rents and payments at my fingertips.

I have talked with the owner and she is eager to answer questions but the answers are off her head and have not asked for any documentation or proof of anything yet.the properties are being rented out for 750.00(2br 1bath), 850.00(3br 1 bath), 750.00 (2br 1bath) and 850.00 (2br, 1 bath)the homes are in moderate condition but have def been lived in hard...

A small bullet to bite in the long run. 

I know that doesn't exactly address your question regarding the 3-plex being considered an investment property by FHA, have you talked with the loan officers about providing proof that your duplex is already fully rented out, to show your intentions of occupying the 3-plex?

She always told me that she wanted me to own this property but she passed away unexpectedly before she could make me a Will I know that is not any good proof.