Not the official photographer?
Then just the 50, be everywhere while staying out of the way.
+1...let's the pro does his/her best.
Although I would love to have a capable "photographer" at every table/group if possible. There are many moments that are missed because there is only so much one or two pros can cover.
I remember placing those disposable 35mm film cameras at each table when my wife and I got married. I was expecting a lot of shots to be bad, but I wasn't expecting THAT many shots to be bad. I'm pretty sure it was not worth the cost of those disposable cameras and the cost of processing the film for what we got out of it. Cell phone cameras are a lot better than those crappy disposable cameras, but a lot of those shots are still no better (as observed from all the FB links from a recent wedding we attended).
I was attending a wedding recently.. did not take my camera but what I saw was disturbing.. 24-105, 24-70 F4, 16-35, on both wedding shooters. Then I saw an audience attendee with a nikon D4s and a 70-200 2.8 (hopefully saved the day). And just by observing the wedding photographers, no offense, made me very worried as to if they will get many usable shots. The moments, which I would consider important (kissing, putting on the ring, etc), they were shooting at the sides or far down the aisle with those lenses. yikes. Since you're not the official photog, you don't need all that gear. But if I were you, I would take the 50 and the 70-200. The 70-200 is definitely a large lens but allows you to stay back and snap some shots. Maybe take the wide angle? Definitely not the flash if you take the 50. Spare batteries and most importantly, enjoy the wedding. cheers