In most cases you don't sell a home to children, the home's ownership is transferred via a change in title.
It sounds to me as though your sons are trying to obtain financing for a loan to buy the home from you. Are you selling at market value or below market value?
Who's idea was it to construct the sale of the home in this manner?
It sounds to me as though you need some alternatives. I am not a CPA, but just a quick search turned up the link below. You should talk with a CPA regarding the tax consequences of transferring ownership this way.