Five years later, a national drugstore chain wanted to build a store on a quarter-block area that included our smallish lot. 

We later found that the cement was originally mixed with salt water & hence the issue.

Last October, we moved out of our first home (a duplex) and instead of selling it we decided to rent it.6 months later it's safe to say we've been bitten by the REI bug.

Better to be more specific  now then mad at each other later.   

That would be a cleaner transaction and they could later sell their portion and not affect you. 

You can always move out and rent it later, but it has to be an owner-occupied property at the time of purchase to qualify for VA financing. 

in case you sell later if that tenant buyer backed out and now you want to sell. 

They all signed the papers in front of a notary, dropped them off the day before closing, and the buyer closed himself at the title company later that day.  

Okay Steve, I will tell you my answer to mitigate acrimony but I choose to withhold specific details and documentation until later because the purpose of this dialogue is to invite open discussion for creativity regarding a common scenario.

I imagine the original note had an assignment of rents and when the owner had to reduce rents or had a vacancy, the bank exercised the assignment and the bank later sold the note to a note buyer, most likely for a discount.