It works like this: pick one of their turnkey-ish houses from their list, or bring your own, get financed for a 50k house with 10k down, pay interest only @ 10% for two(or3) years with 5% accrued interest tacked on to the balloon payment after 5 years with possible 2 year extension.

Must I disclose that I am a non-practicing Real Estate Agent (I currently do not belong to a brokerage) on my lease?

Your low down payment loans will go a lot further that way!

Sent her a notice of non-renewal and specify your reasons.

If you are replacing a rent payment with this then 100% yes bc you will come out ahead.

If you set it up with a car rental service like Turo are likely protecting yourself/car more from potential issues and damage and may be able to keep it off platform and only make it available to your renters (not sure on that last part but just a thought).Also, from a lender perspective it could complicate things if you are looking to refinance one day and have car payments included in the lease payments/on the lease.

I don’t have the down payment yet but I’m sure my relative will want the lump sum at some point.

Seller basically drafts up a contract and decides on a rate and term to calculate a monthly payment.

I have been updating the house and making the mortgage payments in the seller's name (kept his mortgage). 

Figure out what you want to invest in (type of property, what class, college or non-college), what your minimum net income is per door then go from there.