My understanding is that given the couple have commissioned you to photograph the wedding, they are sole copyright owners of the images. Most wedding contracts are drawn up in a way that the photographer can use the images for self promotion but cannot sell the images to anyone other than the client. Thats what mine says anyway (Its a pretty basic agreement), and yours sounds like its similar.

In my case I would need to get permission from the client to sell the images to the venue for use in their brochure. I suppose you could avoid this by stating in the agreement that you can sell the images, but I can only assume that most people wouldnt really like that idea.

I am only a weekend warrior so not sure how much legality is involved in all of this. I just tried to apply common sense when I drafted my contract/agreement. It may not be worth the paper its written on