This is not a "slap them up" construction area like others I've seen. 

I used a hard money loan to purchase this off market deal.I rehabbed the upper two units within two and a half weeks and have a renter already lined up for one unit.

Without it they are not legally required to do that (look up the "blue brochure" https://dopl.idaho.gov/wp-content/uploads/2023/10/irec-Agenc...).

I looked up some info on Bullhead City but there isn't much about future plans.

Obviously need to check zoning and set up costs etc. 

I have sold some properties years ago on lease options where the tenant buyers actually exercise their right and purchased the property. ( I was in the deed.)The reason I am concerned to tie another person’s property up  with the lease option is that people can change their mind, as in the seller.  

This is our first look at DSCR as we've gone conventional up to this point.

Do you look up competitor rates?

You may be safe to get non-commercial F/F adding up to 2 ADUs to a duplex even though by rule this does not qualify (in my area I have never heard of this being an issue). 

Many of those properties don't actually produce income due to turnovers, vacancy, maintenance and damages and you're lucky if they appreciate enough to keep up with inflation.