How to make sure sellers are out by closing

Hi all, I'm in process of negotiating an off-market deal, however, the sellers now say they need money to be able to move themselves and all of their stuff out of the property. They are asking for two weeks after closing to be able to vacate. (We have not signed contract yet, just verbally agreed on purchase price.) How can I avoid this and still move forward with the purchase? Any creative ideas or advice? Thanks.