For starters I'd position your umbrellas at 45s to the group. I'd keep your key about 1 stop above your fill. A 3rd Speedlite behind the group would provide nice separation. I would set my aperture at around f/5.6. That should give you enough DoF. Even in a dark church (or where ever you are going to be ) you should be able to properly expose the background without having to go higher than ISO 800 which will be plenty clean on your 5DII. You won't however be shooting at max sync speed. You'll probably be closer to 1/30th or 1/60th (again, it's really hard to guess not knowing what your ambient will look like). These are ballpark figures and should help you to get started.