I have lenders that I can point you to that would likely be able to give you a better product that will pay off that primary residence loan, or restructure it into one that doesn't take so much long term value out of your equity.

I also have their expenses which are in line with my estimates/analysis.I do not believe the Seller's will like that valuation and I know they are hiring an appraiser.

In this low-inventory environment, the right renovation loan can open up possibilities that you might have passed by otherwise.  

Having your son involved in the loan, title, and insurance policy does have both benefits and drawbacks.

Every two years you have to get it tested.  

In this market small multi families are not traded frequently meaning they do not have comps for these properties.

Just because you and they would have history together and on the same property. 

Off-market, agent-listed, or are you networking with other investors who have deals lined up?

Thus, I’m going thru background and experience checks of GCs, with relevant experience before selecting one instead of using my usual crew which doesn’t have such experience.

Offer a personal guarantee (reduces investor risk if you have the balance sheet for a PG to be worth anything).