Is this a For Sale By Owner listing or are realtors involved. The difference is if the sellers have a realtor, their realtor will force the sellers to obey the contract and tell them the consequences if they don't follow thru. Example: If the sellers refuse, they need to pay the full commission anyway because their realtor brought them a qualified buyer and the sellers accepted their offer. This means the sellers have to pay thousands of dollars even if they don't sell the house. It's in their contract. Another motivating factor is their realtor wants to get paid quickly.
If the sellers have no realtor (For Sale By Owner listing), then you need to contact an attorney. If you are working with a realtor, your realtor can inform the sellers of the consequences but up to a point. Your realtor doesn't work for the sellers so it's a fine line to walk thru. This is why you will need to contact an attorney.