Get the borrower to re-perform.

Network with brokers and agents, run your numbers, make offers, perform your due diligence, before you buy call in experts to look at the property, raise more or have enough capital reserved to cover issues that pop up, which they always do, run your numbers, don't overpay for the property and run your numbers.

Both of you are making critical contributions to the partnership, though it is fair to expect an additional boost to your ownership stake relative to his given your role as the loan guarantor.  

Secondary/tertiary or submarkets just outside major metros typically have low rent appreciation, lower returns, but are generally more stable; like you said, I think poor performing assets in these areas are great to invest in an "up market".

Putting everything into the performance of one property is actually riskier than buying multiple properties with mortgages in many ways. 

We were set to close on our first duplex in the homestead area and were performing our final walk through when we found out the place had been completely ransacked by someone who stole the copper wiring, furnace, water heater, and destroyed the kitchen and bathroom doing so.

I've read books (Turning Distress into Success; Performance Anxiety; Seller-Financing & RE Notes in the Dodd-Frank Era), explored the posts in this forum, listened to @Bob Malecki 's BP podcast episode, and now have some (hopefully reasonably intelligent) questions to ask.

So perform you due diligence. 

@Jeff B. your reply would be relavant if this was a performing property; however, as stated it's new construction.

I' thinking that getting the properties out of my name and into an LLC would boost my personal credit and open up new opportunities of investment for me.