A Real Estate Agent cannot give legal advice regarding "Backing out of the Contract".
Again, see a Real Estate Attorney for Legal Advice.
Usually seller's miscalculation of their finances is not a legal ground to back out of the binding contract even if no escrow has been opened. Opening escrow is required performance of the contract. There are ways to cancel this if buyer fails to perform his obligations in a timely fashion beyond that there is really no legal excuse to cancel the agreement.
Like everyone says....contact a good Real Estate Attorney immediately. Sometimes they can find the flaw in the agreement that could give them a way out.
Good luck ~
They need to contact their attorney immediately. I have had this happen to me, and luckily the sellers were really easy going and let the guy walk, but there could be some legal ramifications so they should get to the attorneys immediately. Here in South Carolina, a contract is not binding unless a meaningful deposit is rendered.