Foreclosure serves a purpose, that is to sever all other interests. 

If a portion of property is rented out, and a portion is used for personal purposes, any reasonable method of allocating expanses between personal and rental use is allowed."

(My comments are for informational purposes only and not a legal advice)

If it's single-purpose (like a drive thru burger joint), you only have historical $/SqFt.If it can be re-purposed easily, vanilla shell with zoning that can handle variety of tenant types, then I'd add some more to the empty $/SqFt.In any case, you're going to need to know sales comps.

In a situation like yours, the sale is partitioned (for tax reporting purposes) between the personal use portion and the rental property portion. 

It's purposely set up that way to NOT penalize you for shopping around.The difference between local lenders and national is generally not small. 

Footnote: while I am a Financial Advisor, and I do welcome inquiries in that area, that's not my purpose for posting this interaction or response - I'm genuinely curious.

If you are looking to put both of you on there for estate planning purposes, there are other ways to handle that :)

He showed me the receipt and he collected a ton of them in a folder which he keeps and deducts all theses phantom bills for tax reporting purposes.

I've been looking at their business card options as something we may switch to for the convenience for accounting purposes.