How should I legally structure all this?

Beside the “subject to” that’s recently become the subject of much debate we utilized  ”no interest short term owner financing”, the “2nd mortgage crank”, substitution of collateral, mortgage subordination, wrap loans, real estate “exchange” (not for tax reasons), sale - lease back, guaranteed rent payments, sale - buy back, land offered in lieu of down payment, zero coupon bonds as substitution of collateral, and a few others that escape my memory.  

I would prefer a Line of Credit product here specifically if it were me but I would certainly lean on other investors in your area on who those lenders are that offer such a thing. 

I will offer cash, and I don't care in what condition it is in or how much you owe on it".1 month later:You get an other letter in the mail.

You will find allot of amateurs offering to do this kind of work but you will always get what you pay for.

They will offer to settle for, say $25,000.I have to see a W-2 or pay stub and I don't care what their credit score is anyway.

It's inexpensive, and they have a lot of landlord resources, legal advice, and more.

Many lenders offer up to 85% on investor financing for a 1-4 unit purchase transaction. 

The company's legal counsel has said a guarantor is not needed, citing the company's annual revenue and an employee, effectively, being unwilling to cut a check on behalf of their employer.

Now your offer of handling everything no longer exists.