Scott has a great suggestion for you... and you won't be disclosing any specific addresses by doing it that way.
Are the sellers homeowners or investors? If homeowners, did they understand fully that they would still be able to market their property on their own, so they are not really losing anything? They may have seen that you wanted them to sign a contract, and might not have fully understood. Perhaps going through the option contract with them line by line would help clear up any misunderstanding.
If the sellers are investors, then I agree with Brian that something sounds strange. Investors typically want all the help they can get in marketing their properties so that they get sold quickly. Did they read and understand your option contract fully? What exactly was their objection to it? I would think that as investors, they would understand that you are wanting to operate within the law in this regard. Like Brian stated, if they can't state specifically what is causing them to hesitate, forget this deal and find some other investors to work with that don't mind doing joint ventures.
