In our lease agreements we have the following statement written into our lease agreement.

My renters in my unit are supposed to have Renters Insurance based on my rental agreement, but I never verified if they got it or not. 

In some cases if you are dealing with a larger lender that is relying more on your financials, then I would see this as a potential problem, but someone truly focused on the strength of the deal shouldn't really care.In the past I have used a joint venture agreement structure to work with partners and it has worked great.

I am in agreement with Russell. 

If a price is agreed to you enter into the purchase sale agreement and wire the earnest money deposit. 

This is the snippet from the Massachusetts standard Purchase and Sale agreement that outlines the treatment at a high level.

Looking for a "rental agreement" Google "vrbo rental agreement" go to page 3,4,5,6 of google.

Make sure you write up some agreement when it comes to cash for keys.You got this.

The challenge you're facing is not related to the manner in which you're financing deals, but rather that at 17 you're yet not allowed to sign a binding legal agreement (AKA "age of majority").Seller financing is an insanely powerful tactic, but it won't solve this... 

Unless you have some sort of partnership agreement spelling out all the various contingencies, just sharing ownership immediately bestows upon the partner instant equity.