Below are some data points:2-story SFH (3b3b, 1,800 sqft): 2b2b (w/ kitchen) on the upper floor and 1b1b (w/ kitchen) on the lower floor; each with separate entrance and only laundry is sharedThe estimated rent for the entire house is $3,500, and a standalone 2b2b house can be rented at $2,800 and 1b1b at $1,800, how should I set the rents if I want to rent the upper and lower floor separately?

Again depending on the shape, size, entrances, and visibility of the land, recommend you immediately Subdivide and sell portions. 

From what I have been told we can build multiple lots (if we wanted) off the other entrance to our land.

If you expand your search criteria, you may be able to find something that has a walkout basement, ADU, or seperate entrance that would allow you to rent out a portion of your property. 

However, the brick veneer in the front entrance, which runs from the ground to the roof on the two story residence, "has not been properly supported with structural repairs," with brick deflections and cracks and repairs needed due to "safety concerns related to improper veneer support."

There are 6 entrances from County roads xxxxxxxxx and xxxxxstreet.

When you de-lead the common areas, I had the understanding that all 3 floors' common area was included on that, assuming that containment was blocked off on the entrances on the 2nd and 3rd floor.

Some basements have the entrance in the backyard that you can walk in and not disturb the people renting from you.

Most of the additions with separate entrances and unit is already in place under same home owner. 

I look for SFH bungalows with a separate side entrance to the basement.