Welcome to Nikonians! I hope your time with us will be rewarding.
A friend of mine recently photographed an even larger group of over a hundred people in a church setting. He assembled them on the floor of the sanctuary and captured the image from the balcony overlooking it. Every face is visible.
Unless you can elevate the camera somewhat above the group, or they are standing on risers or steps, it will be difficult to capture all of them in one image.
He used one on-camera and a pair of Nikon SB800 speedlights that were about fifteen on either side of him on the balcony, pointed at the off-white ceiling overhead. The speedlights were set to manual mode, maximum power M1/1. He was shooting with a D700, using an ISO of 1,500, and a metered white balance of 3,050 K, 1/60 second at F/5.3.
The lighting in the church was incandescent, with some natural daylight coming in from windows along the side walls. He fitted the SB800s with the incandescent gels using the built-in wide flash adapter, which meant the focal length was locked at 14 mm. The gelled SB800s overpowered most of the blue daylight near the side windows, and most people viewing prints will never notice it.
Given the subject to lens distance, it may not be beneficial to use the shoot through umbrellas, as they absorb a fair amount of light, and the effect of the soft, diffuse illumination may be lost.
If there is time, I suggest conducting an on-site test prior to the wedding. You situation may be quite different than my friend's.
Perhaps some of our excellent wedding photographers can offer more detailed advice. I stopped doing weddings many years ago, for a variety of reasons. I admire those who shoot weddings professionally ... In my mind, it takes a special personality that I lack.
Hope this helps a bit.
Let us know how it works.
HBB in Phoenix, Arizona Nikonian Team Member
Photography is a journey with no conceivable destination.