Essentially you are going to have terms in the agreement that will allow you to pay the seller, in this case your relative the $115,000 in full once you decide to go long term financing (if you ever want to).  

If your relative will take the same interest rate or less than the bank you have two positives.

Also look very hard at your own cash flow situation and the worst cases on collecting income from the property to be 99.99% sure you can repay your relatives as promised.

Your LTV and DTI ratios will be impacted by the informal 1st mortgage that you have with your relative, but it shouldn't kill the deal.

And, lend your relatives the money to buy a home.

Talk to your relator or to local investors on how essential this is.

I would consult a PM company and have them advise your relative of what rent they could charge if these tenants hopefully leave since they would have a better pulse on rental comps of properties in similar condition.

One screw-up and your friends and relatives will be looking at you, not your mentor.A few questions, and some comments that are fully intended to scare you:Do you or your relatives know how to evaluate a borrower and his properties?

If your relatives are as nosy as you say where they look at tax records have you thought of a response on why you sold all your properties. 

Perhaps you could have your relative simply add you to the title, or give you an option to buy to satisfy the ownership interest requirement, or put the property in a trust and make you the trustee, or assign you power of attorney allowing you to act on their behalf?