tl;dr:
Get a 24-70 F/2.8 zoom (35mm equivalent), if you're serious about wedding photography. Use what you have until you can afford one. (After that, save money for a 70-200mm F/2.8.)

additional info:
Your question is a bit vague. To just do a group shot, basically any lens will be ok, as long as you can use your feet. However, you want to take into account whether you want to portray the group without context or whether you want to emphasize the group in the surrounding (which you might want to do for a wedding). So sometimes a 50 mm can be fine, while you will use 28-35mm most of the time, and probably even 24mm if you want to catch an impressive builing as well (to increase the percieved size difference of group and surroundings).
To get a close-up with nice aesthetics and proportions I would never go below 50mm (for anything less then head-to-hip), or 105mm for headshots. If close-ups also mean detail shots of the wedding rings, you might end up wanting a macro lens (down the road) as well.

personal addition:
I prefer fixed focal lenses. However, this doesn't work well for weddings, where flexibility is key to capture the event on all levels. If weddings are just something you do next to other things, you can get a set of nice primes that allow you to do anything, but with additional swapping lenses. Since you didn't mention your budget, you might as well go with whatever zoom you have, - subject isolation by low aperture is less important than pressing the shutter at the right time in the right place.