Your loan size will also effect the rate as a lot of the better non-qm financing have loan mins etc.  

Later, she informed me that she is unable to work and, as a result, can only pay some portion of the rent until the end of her lease.

Columbus OH, we work with a Charlotte land developer here on larger sites like 30 acres and up not sure how big but your niche size is great. we do development, licensed general contractor, and build single family and multifamily we have a few new Floorplans every few months and I travel nationally to be an advocate for our market. it's wide open. high absorption potential and only 8 builders who build over 50 houses a year in our market. 

We just made the INC 5000 list for fastest-growing mid-size companies. 

The rental income is the majority portion of my income which is where my problem is , my other work mostly consists of working for my grandfather in the Ag department. 

If a future deal looks similar I may want to change the split to 60/40 or something so I make a larger portion of the profit for doing the heavy work.

Assuming the size/#bedrooms is the same as the comps, my gut would say they'd cancel each other out and you'd be around $1300

The owner may reside in either the remaining portion of the structure or the newly created junior accessory dwelling unit.

I have looked into the DSCR loans but you would still need to come in with a large portion of the down payment correct (the remainder of what is under the 75% loan to rental income )correct?

You are not able to choose only the after-tax portion when doing a conversion.