When we sold one of our contracts we did all the initial paperwork fast. But then we waited and waited for the paperwork for the final sale to come through. The Timeshare Store called us asking where it was, and we told them we never got it!
Fortunatley when they called we were actually in Florida, and we went to their offices and signed everything, and had our check a few days later.
I would make sure that the sellers for sure have the paperwork.
Assuming you really want that contract and want to go thru the hassle. And you have a signed contract you can force the sale if the seller decides to back out. Often time a threat to force the sale will move the seller to complete the sale.