First what I see from your exif.
1. The shutter speed is WAY too slow.
2. The WB is set to daylight??? I think you should set it to auto; unless you know your camera better.
3. Is it possible the church will let you set up some kind of lighting back further from the front of the church???
4. Your 50mm is the lens you have that is better suited. If you rent a lens, I have the 24-70 - you may want to rent it a couple of days earlier and ask the church if you can practice a few shots with it. This lens will not be the cure all answer though.
5. I would take it out of AI and use 1 shot. There are others here more experienced and may dispute this...believe them over me.
Me, I would rent a fast 35mm, as fast as you can afford, all will be much happier. Remember you are using a 1.6 crop camera. (35 x 1.6 = 56mm)
**I do not photograph weddings or people. When I have shot indoors (people) I realized the faster the better the image. Also, depending on how close you are shooting from, watch the power of the flash, you may want to ratchet it down a little.