I mean, don't get me wrong, we have to comp the property...so if you are looking to REHAB the property and make it something different, then you need a rehab loan first and then refinance after type of thing. 

ThanksBrett, we do flips and rehabs and have several lenders in the area that specialize in ARV "style" loans.

Loan: Bank Statement, $5,500/month PITI.

Sounds like their combined income likely beats your other tenants.Your gut is probably your best bet and you need to go with it. 

Tired landlords and conventional loans weren't available.   

Real numbers- purchase 907k,rehab , closing costs, soft costs, 840k, all in 1.747 mil, basis for each unit should be roughly 291kappraisal of each unit minimum 400k , so 2.4 mil if for all 6.I might refi only 4 out of 6, that will cover initial loan amount.

Loan: Bank Statement, $4,300/month PITI.

You're likely looking at a 25% down loan for a non-owner occupied. 

Then you can immediately put a loan on. the free and clear property and pull that cash out to get close to what you need for the ADU. 

I can say from having taught classes on these loans that your contractor will be the biggest key to your success.