Equipment fails - I've been photographing weddings for near on 10 years and I've had at least half a dozen equipment failures over that time. If you're getting paid for this you MUST have a second camera, and even if you're doing it free it would be irresponsible not to have a second body. Rent, borrow, probably not steal, but get that backup.
Take all your lenses. 16-35 may get a workout depending on the scenario. 70-200 will likely be used during ceremony and reception. Given you seem to like primes you'll probably want prime to suit the situation on one body, and a zoom on the other. Weddings are fast paced. If I shot primes I'd use three bodies. Having a 24-70 F2.8 would be easier.
Wedding photography is a profession, not a hobby, and you're messing with what some people will call the most important day of their lives. Stop making excuses and take it seriously.