Realtor messing up a short sale?

[John Smith]

So the owners of the place my wife and I are renting want to do a short sale because they can no longer afford their mortgage payments. (They bought right at the peak and paid twice what the place is actually worth.)
Now we like the place and don't want to move. We were going to buy the place if we could get a good price but the owners have their own realtor who is trying to get top dollar for the place. The realtor's rationale is that a higher offer is more likely to be accepted by the bank. While this may be true, it certainly screws us up.
So a few questions: Does a property really have to be listed on the MLS before a bank will consider a short sale? The owner's mortgage is with Wells Fargo and the property is in Southern California. Should we try to get the owners to ditch the realtor and get a dedicated short sale negotiator to work with the bank? All the owners care about is getting a short sale done. Any advice is greatly appreciated. Thanks!