Have them lay out the process and the costs involved.

However, I can't find sources that layout the details on how to execute them (i.e. paperwork, process, etc.).

Houses pre-1900 often have layouts that are awkward by today's standards, and that would be my biggest concern about resale.

There are NOT a lot of duplex that come to the market in this area (most are under and over layouts not left and right)5.

Especially considering that because of the layout of the space, he crosses in front of mine every time he pulls in or out, has blocked the driveway for months at a time with construction vehicles, and because I split the cost of the repaving of the driveway with him last summer 50/50...but I digress. 

Owners are free to do whatever they want with the interior layout.  

My advice would be to arrange a buyers consultation and lay out your objectives and what you are looking for in a Realtor ask him how he would get you to where you need to be if his answers meet your expectations give him a chance to earn your business and see how it goes.

Based on an abbreviated cost/benefit analysis, I am leaning toward keeping the layouts as-is and avoiding relocating structural/load bearing walls but I would be willing to engage an architect/engineer and invest a little money into better understanding what would be required if I were to make more significant changes to the current layout.Thanks so much!

Original appliances layout ect.  

Demo is done, windows and a door are in, reconfigured bath rooms for a better lay out, plumbing done, got the power turned on.