Upload & Sell: On
By being 'honest' you mean you told them your concerns above, I assume?
Not to be condescending, but what kind of response did you think you were going to get when you gave them that kind of response? I would think that you would just be inviting trouble, or worse offending the potential clients. While I admire you for being upfront, I think a simple 'I'm no longer available that date, good luck' would be sufficient.
Send them one final email, simply saying that you are not available to shoot their wedding, wish them luck, and ignore future correspondence is my advice.