Option 1 allows you to spread your investment across three properties, considerably increasing your rental revenue and accelerating portfolio growth; however, maintaining several mortgages can be difficult, potentially limiting your cash flow, especially if one property is vacant.

Also some lenders will offer this on newer originated loans.It’s not common but I have seen it offered on occasionIf there is a higher default interest rate then I would consider it but if it’s the same rate as default I would not accept it

The owner bought it for cash, so no mortgage.

As I would have to move in at least for a year to assume that rate.

They look at the interest rates and say, rates dropped X% so now it's time to refi.

Is it Cash Flow, Cap Rate, COC, all three or something else?  

At a glance, it's just Quicken 2.0: advertise a great rate, bury in the small print over $10k in junk fees per $600k borrowed.

Cash out refinance is usually recommended if you are lowering the interest rate.

There are less lenders who do this and the rate and fees will usually be higher. 

The MIL has owned the property for 4 years and there is no mortgage (purchased in cash by her grandson; I raise this to you in case there are capital gains implications for MIL and DIL when the latter sells).