Why aren't they ready to close? Are they buying another property? Often there is a chain reaction on closing. I would suggest that if they need more time to set a closing for their purchase that you discuss with your attorney, renting out the apartment to them for X amount of days.
Remember any fees that you aquired thru this, you attorney can get for you back at closing.
Unfortunetly it sometimes part of the real estate game when involves a link to multiple transactions, for one to close. Be patient and most of the time everybody gets to close and be happy. Good Luck, Happy Holidays.
Your agent should be able to let you know what the real situation is. Does the fully ratified contract indicate the sellers having any contingencies i.e. is your close of escrow contingent on a successful close of escrow of their new home or sellers identifying a new home to rent and move into, your realtor should know and be able to explain the comtract to you. Whatever the case maybe, both realtors should be communicating on what the real situation is and come up with a win win situation, at this point your realtor should gather all the necessary info and sit down with you what the next best course of action for you. I hope that helps and good luck!