Quiet Title a Joint Owned Property from Sheriff Sale

[Kevin Che]

I'm looking to buy a property located here in Rockland County, New York. The property is a sheriff sale, with the creditor winning the case by default in court as the defendant never showed up. 

The creditor was awarded around $130k, the defendant had defrauded the creditor into investing in this rental property, when the time came to add the creditors name, the defendant refused and left the creditor with $130k less. After taking the defendant to court, and winning by default as defendant never showed each time, creditor is looking to collect on that $130k, the creditor has a executed a sheriff sale against the rental property of the defendant. 

The ownership in the property according to online search is joint owned, by the defendant and an unknown party. The unknown party was not in any of the creditors suit in court over the $130k. There is no listed mortgage on the property. There is also no valid tax liens or any other liens listed. 

My question is, if I purchased this property, what quiet title issues could possibly arise,  as I would be filing suit against the named defendant whom the execution sale is against, but ALSO another name on the property. I would not be as worried if I were to file the quiet title against the defendant named solely, but am of the other name as they can come and claim interest in the property and is not a husband and wife. Would I technically just be buying the defendant's 50% interest in the property? Or would I be able to possibly quiet title and remove the other parties name.