If your buyers love the house and can qualify now to refinance it, do it.
But, if not, you can play hardball with the former seller who is now calling Countrywide to complain.
You could call them and ask them what their chances of buying would be with a foreclosure on their record? Especially one triggered by their breech of a contract.
You could remind them it would be far less traumatic for you to make your current buyers whole than it would be for them to have a foreclosure permanently attached to every mortgage application they fill out from now on.
I would also recommend you contact an attorney who is familiar with area of the law because you mentioned you have made the last 12 payments on the loan to CW. It is possible they have abandoned their ability to call the loan due to their inaction in calling it when they knew, or should have known, the title had changed hands. That is unless you played some land trust games, then it could be trickier.
However, if they have constructively abandoned their right to foreclose, it is my understanding, they could still go after the former seller who breeched the contract.
Anyway, the path of least resistance is usually better so if your buyer can refinance, do it and just move on.
Also, in the future, include verbiage in your contracts when you buy to allow you to seek recovery from the seller when they do something like this later. It stops them cold in their tracks when you point it out to them.