I don't mean to be discouraging but just to make sure you and the couple are aware of the downfalls of having a non-professional cover their wedding.
This being said, not everyone needs or wants to have wall to wall coverage of their wedding, especially the second time around.
I have done several weddings for friends and relatives and I have always stressed that I would do the best job I could for them but they had to understand that they were ultimately responsible for the decision.
I've never had a major problem with any of these weddings (I haven't had to use the backup equipment I had with me), and the couples have always been more satisfied with the final images than I have (I tend to be a bit of a perfectionist when it comes to photography).
So... Go to the wedding, do the best job for them that you can, and don't forget to have fun!