I believe it was just a flat rate per property per month, and quite inexpensive.

The loan we were applying for is an FHA, which stipulates we must provide a signed lease for our half of the duplex (to be newly rented out) but for the other half which the parents "own" (in reality all three are equally owners of the entire property.) we would need to provide proof of rental income on our tax return, however her parents claimed that so we seem to be SOL.The mortgage is covered, we can rent it out no problem, but the underwriter is saying on paper it looks like she is responsible for the whole duplex and the rent for half of it is unreportable.

I need to research all 4 and compare fees, interest rates, and tax benefits. 

Everything was going fine until he realized he couldn't refinance in this current interest rate environment.

I'm looking at a property for sale, what cap rates are these size deals going for in Jerome Powell's market?

I will most definitely purchase a cost segregation study to nail down what I can depreciate at an accelerated rate.  

However, this can be contrasted to a considerably lower rate in those segments with college degrees and further educational attainment, which is supported by lower median income of $34,748 in 28301 and $54,444 in 28304 compared to $66,778 in 28305 and $61,053 in 28306.

What is the going rate for a 3 bedroom detached?

This is stated in the tax code under Section 168(k)(8) which outlines the bonus depreciation phase-down rules for property acquired before 9/27/17.

She does have good credit and has paid taxes for the last 3 years.