The COC on the 1st house if I am calculating it right would be just shy of 10%.  

You calculated $400/month, but did you account for repairs and vacancies?

Here's a bit more in detail about how rates are calculated for DSCR loans:1.

Looking to do mid term rental in the unit that is left furnished while they are not there and Section 8 in the other units ideally.Just trying to get my reps in with deal calculations.

If they want an off-market property, I even built a BRRR calculator that they're using to feed-in the numbers from the 'B'uy all the way up to the final 'R'efinance part. 

The brokers calculated a jump of 30k in property taxes after sale.

This structural connection between the ADU and the main house typically requires engineering calculations to ensure proper load distribution and structural integrity.2. 

Another thing you should calculate is the after build value.

If lemders were able and willing to add the 2-3% of a buyers broker commission to the sale price when calculating LTV, there would be no difference to any party and the cost of services would become much clearer.  

2-Did you calculate your soft costs?