explored that option but rates are really absurd, makes it a financial death wish.... 

Does anyone know the going rate for price/sq ft to construct a beach house?

She is willing to sign on as the main tenant which means she is responsible for the apartment. my thoughts thinking out loud:the other prospective tenants have income issues so at least in this case I know the rent will be paid. the mother has pretty significant assets (low 6 figures + another 6 figures from sale of the house) if he destroys the property I could go after her for it right?

We added value by re-doing the whole house, installed vinyl floorings, rebuilt 2 and a half bathrooms, re-painted the whole house, replaced all the hardware in the house, installed new lighting, ceiling fans, re-painted the kitchen, and completely remodeled the upstairs.

I would recommend that you lease it from her at market rates in an arms length fashion. 

Anyways, interest rate is decent but not under 5%.

I have equity in my duplex that I would like to leverage, but the interest rate on the mortgage is at 2.7% so I don't want to cash out refinance (considering interest rates right now are in the 6-8% range).

I honestly don't believe anyone should be paying double-digit interest rates for hard money, and I'm on a mission to change that. 

However the rates with that investor are pretty rough right now.  

We over improved our first 2 houses because we thought every little thing had to be perfect.