You want to keep paying cheap rent but get an A-class rental in exchange.

Listsource you can pay per lead or get a subscription. what are you using the data for and what lead types / properties are you looking for?

I will assume his loan and he pays me his mortgage, plus a little extra.

I want to buy the property on terms and demo, build a new house.I want to structure an owner finance deal with him where I either pay him interest only on the lot or no payments for 18 months (or until the new house completes and sells whichever is earlier). 

When buying an apartment building, it's reasonable for the buyer to ask the seller for copies of leases and proof that the rent is coming in, and the lender will likely ask for that same paperwork too (since that's what's paying the mortgage, not the buyer's personal W2 income, ha).

The thing is, she has until the 2nd of July to pay her back taxes, and if she is unable to pay by July 2nd, she will have to file for tax bankruptcy.

She'd have to invest some money to create this set-up. 3) Selling doesn't make a lot of sense, because in this market, she'd end up paying the same for a small place, condo, with less flexibility. 

You can do a ‘cash out’ refinance on the rental home as a permanent fixed 20-25-30 year loan to pay off the Heloc on the primary and most likely the equity line on the primary permits a ‘re-draw’ to utilize again. 

Incidentally, no one is paying us to be extra-special nice to you while we do it.

They would work enough to pay rent but attend school enough to graduate.