Need Help in Sub 2

I do mostly short sales and rehabs so excuse the possible simple nature of my questions.
I have a seller who has asked me to assist with finding investors to buy his 4 properties. He is willing to keep the debt in his name (sub 2) but needs about $10,000 to walk away ($5,000 to bring payments current and $5,000 to him). We have sourced a few investors who are crunching the numbers and it looks like at least one will take all 4. There is about $120,000 in equity among all the properties. The investor/buyer is willing to pay us for 1/3 of the current equity. We are willing to take a large part of this payment in the form of a 2-3 year note.

A few questions:

Should we put an option on the properties to get an equitable interest in the properties?

What kind of documents should we be using?

How do we make sure the bank does not get notice of any change as the buyer puts insurance and taxes in his name?