It would be nearly impossible to prove out price or pace here, meaning we would likely not be able to get corporate approval for the investment. 

I am approved to use VA loan at 5.5% guaranteed.

I know I will need to get some legal advice, but I am really looking for some input on where I should even start. 

Hey,If "building class designation" is the same as zoning, then this seems like it can definitely be appraised as a two family, with both the legal and actual designation as a two family.Depending where in NYC, that may not help your valuation, as primary residences sometimes sell for more than investment properties, so check that out before challenging the appraisal and definitely before paying for another one.Double check all this with your lender/broker as well.Best of luck!

Adding to what Greg said, there are lots of buyers who aren't pre-approved or will make an offer and then not be able to get financing wasting the seller's time.

You can do a subject to transaction but that is not legally assuming the loan.the banks got rid of assumable mortgage long time ago. 

If you're licensed and acting as a fiduciary, you are required to use the TREC promulgated form or another form approved for use by TREC (ie TAR) unless the seller or buyer or their attorney requires the use of another form. 2. 

That will dramatically change the nature of the wholesaling business with the legal compliance factor that agents need to comply with.

I finalized the property on May 3rd and they told me they already have a tenant ready to move in (they did not take my approval or anything or even informed me their background).

Take control of the situation yourself, and if you want her out, then give proper legal notice.