When I was shooting weddings a few years ago, I would use a wireless mic on one camera (WITH FRESH BATTERIES), usually hidden inside the lapel of the groom, or officiant if the officiant is willing. Secondly, I would use a good shotgun mic on the stationary camera in the front of the church for backup and sometimes as an ambient mix becuase sometimes the wireless mic is muffled from the position on the person wearing it.
I would also suggest attending the rehearsal to ask questions about mic use and camera placement and to inform the participants of these issues before hand.
Best of luck in your shoots.
John