I would use a bedsheet or white nylon fabric hung between two
lightstands as a main light, another light high and behind my subjects
on low power as an accent light and the third light illuminating my
background.  You would probably not need any other light modifiers on
your lights unless the accent light was not covering your 8 person
group evenly.

Main (possibly umbrella), fill umbrella, background light (with snoot as needed)

I suppose you mean you need to lay these images out so they co exist side by
side and the images all have a consistency, the color balance and density
doesn't jump around.  Or do you mean that each face, whether its a dark skin
or light skin looks the same?  kinda doubt that second one.

you can do whatever you want with the lights, consistency comes from steady
exposure,  are you using any auto functions of your camera?   One woman that
ran a service doing digital processing was being run ragged by one of her
clients who shot lots of real estate agent portraits and stuff like that,
the color balance jumped around a lot.  first thing was how was the color
balance set?  if you use auto balance, it will adjust widely if you have a
subject wearing a strong colored suit or shirt, like so many real estate
women do.   And auto exposure can obviously cause similar inconsistencies
with density as the sensor 'sees' more white shirt or dark suit between each
exposure and pose change.

so now we deal with lighting.

the softer the lights the less specular highlights the easier the skin tones
will be. especially if you have black subjects, dark skin reveals bad
lighting very well, and revelles in good lighting.

with a large diffusive light source you can expose for the central value,
IE: a gray card and get excellent detail both the highlights and shadows.
This means that whether you have a black or a pale white subject you will
get proper skin tone, in fact you will get detail in a white wedding dress
and a black tuxedo.

I'd hang a scrim of translucent fabric, rip stop or sports nylon, bounce a
couple heads off a side wall and through the scrim, use a couple sheets of
styrofoam insulation panel if you need a white wall.  use another for a
fill.

use the third head for a hair light.

the wider the light the more even and consistent the lighting will be across
the subject field, the person on the left side will get a more similar
quality of light and a more similar exposure as the person on the right.
This is 'depth of light'

a set of scrims, curtains and reflectors will cost less than a few
softboxes, umbrellas and will likely serve you better.

the reply is echoed to the z-prophoto mailing list at yahoogroups.com

Two large umbrellas (reflected) placed slightly out from and behind the
camera and slightly above head height. Have them 'crossing' each other to
feather the light out across a large group. I'll assume you will not be
lining up eight people in a line, but arranging them according to height,
clothing, importance, etc. (watch out for shadows on faces) It'll be fairly
flat and boring, but if it's a corporate type shot, it'll serve it's
purpose. The third light will be on a floor stand behind the group with a
normal reflector or smaller brolly, assuming it won't be full figure. I
would shoot the single portraits separately with a little more modeling,
adjusting one of the brolly's.

Another option would be to get a very large softbox slightly to the side of
the camera with a brolly opposite for fill. This would give a little more
modeling but you may get some fall off unless you group your subjects in. If
you are lucky, this may also serve for single portraits without adjustment.

If it's corporate, your biggest problem will be getting them to turn up at
the same time. Good luck!