This is not an uncommon scenario for blended households - He owned a house and she owned a house and they got married and never bothered to change the deeds. 

He's investor focused, so he's pretty experienced with the B lending market.

The blended rate of these two loans is going to erode the cash flow and become a barrier for the investor/buyer to capitalize repairs and handle vacancy loss among other obligations.  

You can either increase income by finding income that was under reported or inaccurately reported on the loan or you can find a coborrower to blend the income and lower your debt to income (DTI).You can pay down debt that has the highest payment relative to the balance so you can thin out the DTI.You can slap a MCC on that loan which is a mortgage credit certificate (if you're a first time buyer) and this is an owner occupied loan.

I think it's a fabulous idea but me and my fiance are a blended family of six kids (the real life Brady bunch 🤣) so it's hard to find enough space.

We spent October- December 2016 getting our financing in order, finding a realtor and then a second when the first didn’t work out, finding a property manager and then a second when the first didn’t blend well with us and reviewing listings online.

Based on the range of these GRMs, choose a number that seems most appropriate (some appraisers will simply average them all together - others will just choose a number) ... take the GRM value you've decided to use and multiply it by the monthly rent you expect for the duplex you are pricing out - this will give you your "income approach" value.Now, you look at the two values you've just generated and use your best judgement as to which is most accurate - or it might be a blend of both.To give you a real-world example of this, some clients of mine just closed on a duplex in Raleigh ... the appraisal came back with $468k for the sales comp approach - $594k for the income approach - and $480,200 for the replacement cost approach ... the appraiser selected $468k as the market value.Hope I made this clear enough for people to follow and understand...

You're blending personal and investing.

They are usually looking at higher quality deals where cap rate is lower but with value add and rent growth they can blend higher in a short period of time.

When you house hack you are always blending your living situation with your investment, so you sometimes have to sacrifice a bit on one or the other.