After talking to another family member they said they would be willing to go in on the duplex and offered to pay the $40,000 down payment and help with any repairs but they want to be "partners" or "own" a percentage of the duplex.

It may sound nice to pay a 5% management fee but the extra fees can add up to be more than the other company that charges 10% with no add-on fees.

If the deal is right you can use hard/ private money to finance the home purchase and some or all of the repairs, then do a cash out refinance to pay off your hard/private money. 

Their target audience are professionals with cash don't don't have the time or desire to become educated and are willing to pay/forgo some revenue for a experienced investment relations firm. 

I wouldn’t be excited paying much more than the land value.

Option 2: We pay cash to build a small 2/2 cabin initially.

The property isn't 'cash flowing' but our renters downstairs take $2,100 off our $5,700 mortgage so that comes down to my fiance and I paying $1,800 to live here.

It may be worth having an experienced professional helping you and you could always try to get the seller to pay your agent’s fees.

These boxes are sold on Amazon, and I can pay to have them shipped to him.

Is it better to sell, pay off mortgage and capital gains and take the cash to invest in another property or is it better to refi/ETO and take the cash to invest in another property?