Not sure exactly what your question is.... If you're asking whether or not you should sign a new contract before you get a copy of a Release and Cancellation of Sale signed by the Seller on a previous contract...
It depends.... you need to contact your Realtor that is looking out for your best interests to see if it is advisable to proceed with signing a 2nd contract when you haven't yet been released from a prior contractual agreement.
Call your Realtor. If you do not have a dedicated Realtor assisting you then you MUST pay an attorney to give you the best advice.