If I couldn't see possibly living in it, I'm not going to try to get someone else to. 

@Kevin Zhang what I did not see in your story was "who is living there now?" 

They usually know what’s been approved recently and can give you ballpark costs for a duplex build vs. other options (like adding a rental unit/ADU).From there you can run the numbers: would it make more sense to build, live in one side and rent the other + your current house, or sell off part of the land and roll the proceeds into an existing duplex somewhere else?

I’m opening a slot for a partner on this live deal (~$150K–$200K SBA injection + EMD).

If you’re planning to live in the property, FHA 3.5% down let you get in with less money down and you can still house hack if it’s a duplex, triplex, or quad.If you’re buying as an investment (not living there), most lenders will want 20–25% down on a conventional or DSCR investment loan.

I live in one of the units.

You fortunately live in a part of the country where a lot of ppl vacation, so you have your pick!

They can help locate, renovate, and manage your property whether you live in the area or not. 

But we got a request saying that their kid lives next door to us so there would be 4 adults.

If numbers show negative as you live in it that is going to happen on any deal.