Adding acreage to property valuation?

[Brian Christensen]

My parents own a 0.58 acr business property on a main road that is growing. Their building is in poor condition. The neighbor has 0.17 acr with a run down non approved duplex. Owners are a dad and a son who own 50/50. Son needs money and is offering to sell us his percentage on the home. Area is really booming with lots of construction  

Complex, but upside could be nice. Just trying to think how this could work and need someone with experience. In the past my parents have been approved for multi family but did not proceed. 

Endgame: make condos or try to just keep the rental. 

Thanks