@Isaiah Elysee, I think your spreadsheet and assumptions are generally OK.

Yes no assumptions.

Your assumptions that you can just keep paying her loan after her death are naive.

I had been looking at a 12plex if that makes any difference.Is that easily found information if we wanted to propose a loan assumption or seller financing. 

My assumption is that a developer could go vertical to build mid-rise multifamily, building approximately 27.5k sf.  

While that allows me to make certain assumptions about the property, I can't really decide whether it's a good deal just based on the information alone.

If you sell before owning for 1 year, you will pay short term gains, so there is benefit in holding for at least 1 year.2) Are you sure your assumptions are correct?  

I suspect your assumption is correct that there are 2 legal units and the space for the third unit is legal, but the unit is not. 

Did those mortgage rates have any assumptions tied to them such as loan value or credit scores?

My assumptions are that current Rates are at their lowest and not expecting lower rates in 5 years for refinancing and my goal is to keep the duplex for the long term.let me know if there is anything I am missing or should consider