In doing so, they separate the home and the land as different investments.

Make sure you keep the money separate and do not use anything for personal use (buying a car, vacation, personal home, etc.)

I live in the main home and have a separate 2 BD 1 BA pool house that I rent on Airbnb. 

Or you can also look at basing the property value off NOI, which is a separate subject.

Some of that it seems that it is left to individual lenders to determine but I have another conversation coming up with a separate lender that hopefully they can shed some light onto it some more.

(Not separate entrances & the tenants usually share laundry) What would you recommend?  

However I see that if you can structure this deal correctly you can qualify for a long time capital gain.Tips to get capital gain treatment on the sale: A) If you have actual investment property and you are dealer: -Maintain separate book-Document intent to hold the property as investment property in Minutes or other document-Report expense as investment expense on tax return-Also use separate entities.Using controlled entity to get capital treatment on land:-it is important that the sales price reflect the property's actual FMV at the time of sale. the formalities of a sale must be observed.

Although if we were the ones renting out the unit, that would be a separate unavoidable fee.

Do you find that it would be helpful to have a completely separate bank account # for your business and another for personal? 

Their kitchens are next to each other separated by a wall.