There are a few things you could do, depending on what the configuration actually is.

I own 2 vacation rentals a few blocks away and this was great opportunity to add 4 units in a creative wayMost investors didn't identify zoning allows STR vacation rentals and the property is already nicely configured for residential with 4 x 500sf units, which will become small 1 bedroom Airbnbs How did you find this deal and how did you negotiate it?

You don’t give any details or the address so it is either an unpopular size/configuration or location.

My question is, how do I configure a deal with partners on something like this.

This is unique property and I too am surprised a lender wants to deal with it as it's configured.

I'd also recommend Avery's book. also read it. again, it doesnt show or go thru actually in the platforms, where you create your listing, where to set prices, makes sure have this 1 item configured, make sure you do this thing, etc. the books you guys are mentioning are more on strategy, not actually using the AirBNB and VRBO platforms themselves

Since closing, I have spoken with neighbors and tenants who have lived there for a while, and learned that the plumbing is unique because it saved money and time to configure it the way it is configured.

Some self-directed IRA plans are configured to allow for investments other than the stock market, such as real estate.With a self-directed IRA you are not borrowing from the plan so you can invest in real estate.  

Replace all doors and update the configuration of the owners closet.

Let the new configuration of your equity in the SC property pay for it...and more.