OK. Not gear related but here's my two cents worth. If they want to have photographs worth keeping they should have a pro do it. You have never done one and there a lot of novelty shots and standard ones that will not occur to you. Folks who do weddings regularly get a rythym and they seem to just flow through the day no prob. It will be awkward for you and you may fumble through a bit so you might have some stress from it. If you have been invited along with your wife be prepared to spend the day apart from each other as, being the photographer, there ain't much time for socializing. You will view nearly the entire occasion through a viewfinder. It Is hard to participate that way.
That was all kind of negative, but if it is your intent to SHARE the day with your friends and your wife and enjoy yourself fully, leave the camera at home.