This is bad math, once most people factor in their income tax bracket. 

All of these factors/considerations impact each other to some extent and its impossible to know whats possible until everyone in the group is clear on what they need/want this to look like.Either it sounds like you're on the right path with the line of questioning. 

Building a new location, development profit., B. 

This article presents three key factors to consider before deciding that now is the time to sell/exchange: 1) regulatory, 2) economic and 3) personal timing.1.

Your limiting factor is the amount of INCOME you can do this with and for HOW LONG you can do it. 

Quote from @Bear Geiger: At Little Bear CreekProperties, we specialize in developing large tracts of land into individuallots for home builders in the Raleigh, NC area.

This was found off market, we have developed a process to find off market deals.

My developer client successfully defended the initial challenges and settled on this having PE rights, so he shifted the site plan to avoid the issue.

If you are not attached to the duplex, could be a good time to sell to developers who want to convert to individual condo units.

Plan is to develop and sell the homes.