The fourplex is the best number configuration due to not be 5 because that would be commercial.

I bought a 4 family in 2016 and the one right next door with very similar configuration sold this year for 27% more than I paid!

Just depends on the configuration of the plumbing and how it's set up. 

As their Grandfather built it, it has a very strange configuration which isn't marketable but it's sentimental to them.

Yes there are lots of different ways that you can configure google voice.

Take any specific home configuration & sqft and then compare that to regional variations; they will not compare at all as this is a difficult blackbox problem to solve (ie adjustments must be made from outside the computer)Any realtor relying upon these systems is incompetent and lazy. 

My SFRs are 1/10th the effort vs the park that is lot rent the prefered park configuration.  

I’m looking to get a quad configured as an over under.

The building(s) configuration is immaterial.Let me add, the two buildings LOOKS ripe for subdividing into 2 APNs to enable selling one side at a time for tax considerations. 

My 2 cents when building a custom build is definitely to use a good investors agent who is familiar with the product as your buyer's agent and DO NOT go directly to the in-house agent unrepresented a when you do so because 1) investors agents know the most profitable configuration and location. 2) Most builders agents are like residential agents and often don't think about what the best approach is for an investor. 3) Investors agent will do everything to look out for your best interest, and they cost you ZERO money for all the insights, market knowledge, tips, shortcuts, tax saving strategies, etc that they can give you.