The sale was held up because until probate is properly completed, there was no legal authority to sell the home. And if the forms were done incorrectly, probate could not be completed until they were corrected. While this was very unfortunate, it is a consequence of your sellers trying to buy a home that was in probate--if it was in probate, it again was not subject to sale at that time, and so was subject to delay if the process dragged on for any of a number of reasons. This was a foreseeable risk of the situation.