Almost all purchase contracts have a contingency related to the ability to get financing.
They usually specify the loan amount and interest rate. If the buyer is unable to get financing for the specified amount and/or at the specified rate, they are released from any contractual obligations.
However IANAL and I haven’t read the contract that the buyers signed. If I were them, I’d reread it and see if there was a contingency for financing. They might want to spend a little money and take it to a real estate attorney for review.
Maybe now they’ll be a little less impulsive when they plunk down money to the builders chorus of “You better get in on this now, they’re going quick”?