Prep for my first whole sale; extra lot involved

[Sally Primus]

I stumbled into a situation that could potentially be very good, but I could use advice.  This isn't my first rental property, but the first I would obtain like a wholesaler myself.  A friend from high school contacted me about how her parent's have a rental in my town.  Their long term tenant moved out and they want to sell because their health is declining.   Their son occasionally helps to try to fix it up but lives out of town and they are significantly social distancing due to Covid.    They also own the vacant lot adjacent to the property.   The neighborhood is probably C+. 

My questions are: how do I approach the conversation that the goal is to help them get out of a stressful situation as well as making a good business decision for myself? What do I do about the extra lot? It is a separate parcel on the assessor's website. It is 72 x 126 feet, and I wonder if I should try to get that as well and maybe build a SFH or duplex on it in the future. Is it worth building in a C+ neighborhood? The nicer houses in the area have sold recently for $110-120k , smaller houses that need fixing up go for like $50k.

Thanks!