How many have they run at a single time?

@Trevor McCormick to piggyback off what others have said, determine if you are trying to maximize it as an investment or utilize it as a vacation home you will STR to help cover expenses, as this could dictate which type of property you are looking for. 

They have a bigger single family home and a tiny home on the property, but there close proximity and shared driveway present functional problems that are undesirable for guests. 

I'd be surprised if the complex doesn't have individually metered units so you may be able to eliminate the utility expenses unless those are for common areas like walk ways, parking lot or laundry.

By utilizing section 8 income we will turn it into a property that is insured beyond belief and make over $ 418,000 gross $320,268 net.

Best of luck on your continued journey, HELOCS can be a great tool to utilize untapped equity in a house.

The cashflow should cove ALL of the expenses for the primary (mortgage, taxes, insurance, utilities, etc) AND put money in their pocket.

No - but I'd say about 90% of my borrowers/investors utilize an LLC for what it's worth. 

My vote is if you are going to continue to buy, you need to utilize leverage.

There are quite a number of things that can make utilizing an FHA loan more difficult such as more barriers during appraisal, appearance of low qualification/little cash, typically longer closing period, likely higher interest rate, and PMI cannot be dropped without a refinance if 3.5% down.That said, just chain 5% down conventional loans, and make sure your duplexes pay for themselves.