I'd ask them to consider hiring someone to be honest. Not because your pics won't be good enough, but because you're gonna be stressed as ****.
You'll be able to handle the ceremony*, group shots and most of the reception* without an issue if there's sufficient light. The problem comes in with the bridal shots, creative shots, first dance etc. There's a technique to those which aren't just straight up photography, especially if you have a less than flattering venue, bad light etc.
Which 5D are you hiring? Also, make sure you're getting the MKII version of those lenses, I've heard that the 24-70MKI isn't good at all.
*don't forget that the bridal party will be making entrances into the venues. You're going to need to nail the focus on moving subjects. Same with the first dance, but in low light.