Tell them that their lawyer should have pointed it out to them, and if they went on the cheap and failed to hire a lawyer, then that's their problem, not yours. Tell them that you purchased a house based on your house being sold and if they are not out in two weeks as called for in the contract, you will sue them for "specific performance". Either way, they are obligated to buy the house and fork over the money. If they express a stinking attitude that indicates that they don't care or they think they can get away with it, have your lawyer handle it - immediately.
Certified Paralegal, with 25+ years' experience & with Real Estate law experience.