Your other options are to sell it or give the lender back the property. 

If you sell them, it just means that you cost basis is lower, and you earn more profit (which was the point of doing the labour yourself)... 

I'm not exactly excited for my funds to be tied up for a year while the house is being built but I could borrow against myself (TSP - government employee) or sell some stock/use some of my cash ~$130k.

@Chris Seveney is normally correct here in that "most" people making 6-7 figures are simply selling courses. 

this area is appreciating substantially if you can buy bmv, or fix the duplext and sell in couple years. 

Your debt service will also be lower which helps avoid getting pinched by unexpected expenses and being forced to sell.

Will your identified markets be an easy or difficult area to sell once it’s time?

I have a multi-family property for sale right near Brighton beach that I thought would sell fast but I'm having issues finding investors for it.

You would be paying back the loan via renting and refinancing or selling the property and paying the money back .

The other owners would sell you their shares for the value you agree on, and the loan funding (your new debt) would be their proceeds.