I'd use the longest lens that gets everybody in. Wide angle will make the outer people look wider than they are - which you can compensate to some extent by compressing the edges, but best avoided in the first instance. If you have limited space, see if three layers of people will keep them tighter - it will have the advantage of keeping the finished photo closer to a standard frame size rather than a pano crop. But compose to a standard frame anyway.
Check your lenses for edge to edge performance, f5.6 to f8 is likely the best for this - and as stated, will increase dof, though if you are back from the group dof is not likely to be an issue.
Tripod for group shots can be an advantage as you can watch people far easier when stood to the side of the camera. Stand it on a table if necessary.
Have everyone on the front row synchronise arms - holding both hands together on laps is safe.
Safe, I hate safe. Get them to pick their noses, or better still, the nose of the person next to them. it will create a far more memorable shot.
Here's a rig from a graduation ceremony - note the two cameras, I think camera 2 was for the hat throwing shot. Also the precarious three chair tripod extension! He was a good 40 yards back from the group. The flash was for fill as it was very sunny day.
Here's what he was photographing. I was slightly closer than he was, 40mm for this shot.
Here's my fave group shot. Go to a good location and the poses and expressions don't matter. This one was 17mm, way too wide! I was elevated and stood on a chair to get the line of waves clear of their heads. Looks great as a double page spread at 40" x 20" in their album.
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Wedding and fine art photographer based in the Lake District, UK