You can use ANY lens for wedding group photos, that depends on how big is the group, how much space you can work with, what kind of effect you want to achieve.
if you already have the lens, you can shoot some shots at 14mm, 19mm and 24mm, that should take you more than a minute or two to complete unless you set up a tripod, you should able to know what is best mm work for you.
Bottom line is, try it to find out. All you need is just one or two person shoot in portrait view at various angle to understand how aggerated the distortion can be. U might need a little more time to adjust to mitigate the distortion.
I use 12-24 for group shots and always try to use 24mm if I got space for minimum distortion.
For larger group off course u have to use as wide as possible
, in your case 14mm, but later u absolutely have to do lens correction, nobody likes to see their faces stretched..
Just some clarification on the distortion issue with ultrawides:
The common problem with group shots with UWAs is not because of barrel distortion. Even well corrected lenses will have the same issue of stretched faces at the edges.
This photo shows the effect:
Don't want the egg-faces? Don't get too close when shooting groups.
Technically, the effect is not a problem with the lens -- the lens and camera are reproducing the image as seen from their viewpoint (too close!). If you zoom the example image above till it fits your screen and move your eye close enough (where the camera would have been, to scale), the faces at the sides began to look 'normal'. This works better with prints, cause most LCD screens don't have a wide enough viewing angle.
It's similar to shining a torchlight perpendicular to a wall (you get a nice round circle of light), then tilting to the side (the circle gets distorted).
Some references: http://toothwalker.org/optics/distortion.html http://wiki.panotools.org/Projections (see the bit under Rectilinear Projection)