I can't tell the timeline, but there is a chance the loan officer did not make a mistake and that underwriting for this company is where the final say is made on outstanding loans like that.

You would also need to get everything in order on your end, things like your entity documents, asset statements to verify your downpayment/reserves, make sure there are no outstanding liens/judgments or accounts against etc. 

Could a title agent be able to identify which properties have outstanding debts from previous tenants?

There are many areas that will give you outstanding appreciation if you buy the right property. 

I ignore credit score but look at credit history.. number of outstanding accounts..how have they paid their accounts in last 3 years.

Also, make sure your property is up to code and doesn't have any outstanding liability issues.  

Having a duplex is great experience owning a property and being a landlord - and that's the experience you need to get under your belt you can't get by standing on the sidelines.I don't know your area and if this is an outstanding deal, but I am rooting for you to go for it and get your first step in the door of real estate investing.

When you file the TDA you will be required to pay all of the outstanding taxes and fees in order to get the process started.My understanding is that the property will then go to a tax DEED auction.  

Since he's been behind on payments, my friend said that he will deduct and outstanding payments from the $50K to cover the debt service.

So far its been an outstanding experience as both @Joshua Andrews and Scott are both highly experienced, self starting entrepreneurs with realistic goals and enjoyable integrity.