So, my opinion (Not legal or financial advice) is, do whatever you need to do to put money in the bank so you can make this a cash transaction.

I've thought of inquiring with online lenders such as SoFi, Lending Home, etc.

http://www.nolo.com/legal-encyclopedia/bankrupt-te...I just googled it and learned quite a bit.

So that's cool :) Considering the situation with the sale and comparing the contract options, I would be comfortable doing a purchase agreement on this with some legal verification.

Airbnb has responded to my request that they cannot intervene as this is an "offline arrangement" and they are an online company.

The aggregate UPB calculation does not include the mortgages and HELOCs that are on the subject property,the borrower’s principal residence,properties that are sold or pending sale, andaccounts that will be paid by closing (or omitted in DU on the online loan application).

So my question is, when partnering with an investor/friend/family member how do you legally set up the purchase to ensure cash flows are paid out as agreed?

In Seattle this is no longer legal. 

The buyer is a partner in another successful business, and does have income, but is refusing to use his other income to pay the debt.Current debt is about $180,000 with interest as calculated if the note was performing; however, there are provisions in the note that it goes to maximum legal interest if it's in default, so with that plus late fees, it comes to more like $220,000.I've had my attorney review the note. 

everywhere I look online it says 20% down for investment homes but we are being told by all lenders it's 25%.It's a duplex in Washington state.