It's correct that only the owner of record (the person in foreclosure) has the legal ability to sell you the property. An exception would be if the owner filed bankruptcy (BK) and the house is included as a part of the BK estate. In that case the court and trustee control the property.
In any event I too advise you to seek a local agent who is experienced in dealing with foreclosure (not just short sales). The owner will need to file adjournments with the sheriff and possibly appear before the Chancery judge for more time. And you will need to know how to purchase a preforeclosure and move quickly if you want to get this done on time. Hence the suggestion of hiring an experienced realtor.
Btw, the situation you give to us doesn't necessarily denote a short sale unless the owner(s) owe more than the house is worth. So if the owners owe (for example) $100k and the house is worth $200k, then likely this won't be a short sale. All short sales are (generally speaking) preforeclosures but not all preforeclosures are short sales. You need an agent experienced in preforeclosures, not just short sales.