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| p.1 #3 · Need Help with Lighting Placement |
The first thing to do, if you haven't already, is to check with the officiant doing the ceremony to see if flash is permitted during the ceremony. In some churches the actual ceremony must be shot by existing light only. A tripod, slow shutter speeds, wide apertures, and high ISO settings are needed. With the cameras you list that shouldn't be a problem. Weddings aren't sporting events, so subject blur isn't much of a problem if you time your shots properly.
Where the strobes will come in handy is during the reception where you and the subjects will be more animated. If there will be dancing you'll want max-sync shutter speed and smallish apertures to get good depth of field for sharp focus at the closer distances.
Crossed lighting isn't usually an issue during dancing; it's part of the "dance floor feel," so having a light in each corner is fine.
For the table shots, you'll be best served by a Speedlite in ETTL mode (and camera in Manual mode in my opinion, though others use Tv or Av), with the Speedlite on a bracket if possible to get it higher off the lens axis.