We're hung up about who owns the copyright in the wedding photos. You say the photographer "relinquished" the copyright. Did he assign the rights to you? If so, why is he posting the photos and selling prints? We have a feeling he didn't assign copyright and that's why he can still post and sell the pictures. If we're right and the photographer still owns the copyright, then you have the perfect (and most pathetic) excuse for not duplicating the DVD -- you could be sued for copyright infringement.
For the sake of the happy couple. We're not sure how you arrived at the 20% figure but we wish this matter had been discussed before hostage negotiations were commenced over the wedding DVD. Regardless of who owns the copyright, we hope you follow Dr. Phil's advice (See #4) and we also suggest that you consult with the bride and groom before making any decisions (as they are the ones who will suffer the most from any resulting squabbles).