I currently reside in Ohio where I buy SFR rentals and do a couple flips a year.

Buy that if want, it's probably closer to the 3-5s.  

He usually buys in C neighborhoods and has to do heavy rehab, but he's a construction guy that also runs his own property management company, so it's 2nd nature for him.

So even if you had a buy out agreement negotiated up front and execute that buy out agreement, the bank would still require him to be guarantor unless something drastic changed on your side financially.The best scenario here would be to purchase and rehab the property using a hard money lender or bridge lender.  

This would likely take coordination with a tenant at some point - (ie - plenty of notice to them that they must vacate in order for you to sell the property)Since your current home is free and clear -  you could do a cash out refi or take out a new mortgage on the new house to be able to buy your paren't house and pay off the mortgage.  

Since this is a real estate forum, I'd just clarify what someone could buy the real estate for and what your lease terms would be.How many sq ft?

Buy your Aunt out first 

Focus on analyzing properties and starting small, like house hacking or buying a single-family home to rent out rooms, while ensuring cash flow and maintaining an emergency fund.

My goal is to buy one rental per year with price between 150k-250k for the next ten years (if i get to keep my job). 

I've helped people with SBA loans to purchase real estate for a business, but for buying rental real estate, the DSCR loan is a much better option.