General Suggestions
1) Set and manage expectations. Discuss with the bride before the day of the wedding what she wants out of the family formals. Give her an idea of what to expect the day of. If she knows ahead of time that you have to put up a few lights, then it will be no big deal.
2) Bring/hire an assistant to set up the lighting while you organize the groupings.
3) Better yet, set up your lighting and store it in a back room. Then when it's time for the formals, simply bring them out and plug them in (if need be). Again, an assistant here is extremely useful for making this process as quick as possible.
4) Do a quick check of the location to make sure you have access to a power outlet, if you need it. It's very cumbersome (and not as professional IMO) if you need to drag out a bunch of extension cords to plug in your lights. We eliminated this problem altogether with a portable power source, the Vagabond II. Alternatively you can just use a couple Speedlights fired into umbrellas.
5) Use a radio trigger to fire the flashes. They are dependable and wireless. Keyword=wireless. The less wires and clutter the better. Not only does it look better, but it also reduces the number of cables for someone to trip over.
Our Setup
We use a pair of AlienBee 800's with umbrellas and Cybersyncs for radio triggers. I do make sure to put a receiver on each of the AB800's. You really only need one since when the first light fires it will trigger the other AB800. However, we don't want the lights going off any more than they have to. It can get very annoying to the B&G and family because people will take random shots whenever they feel like it, and if someone is looking right at the flash then it blinds them. (Even if we ask them to not take flash photography)
To that point, we do announce at the beginning that we need everyone to hold off on any flash photography while we do the formals. This keeps everyone looking/smiling/paying attention to us. I have no problem with family members grabbing a quick shot of the setup, just as long as it doesn't interfere with making this entire process as quick and painless as possible.
If you prepare and can move people in and out quickly, this process should only be 15-20 minutes.
The typical setup is to have one light on either side of the camera, anywhere from 30-45 degrees. One light is the key and the other is fill, although there is little difference between the output power. Usually one is 1/2 power and the other is 1/8 or 1/4 power. This makes it quick and easy, and almost failsafe whether it's a large or small group. Umbrellas are important as it softens the light and feathers any shadows. And a calibration target is also important as then there is no color correction needed in post.
I've seen some pretty complex formals using backlight and hairlight, but in the end, the only people that ever buy these shots are the family, and they are typically the traditional sizes of 8x10, 5x7, or 4x6. So we stick with simple.
Takeaway
Based on my experience, I have found the family formals (FF) to be an extremely important part of the day -- regardless of the pictures that come out of it.
Often times this may be the only time you interact with some of the extended family members. And the FF time is something that people remember and talk about. So if it's a positive experience, then that often translates into positive word of mouth for you.
Seems like everyone has a tale of a negative FF experience and many times people dread the FF pictures. They view it as a 1-2 hour nightmare. Exceeding their expectations by making it quick and easy provides such a stark contrast to any negative experience they had that they it puts them in a better mood for the rest of the day. Then they are more friendly and relaxed around you, and realize you aren't anything like "that guy" or "that lady" who they had a negative experience with.
And guess what comes out of that? Happy guests and family members. Referrals. More sales. Compliments to the B&G that reaffirm their good decision to go with you.
My point is simply that the FF can be something that sets the tone for the rest of the day, so make sure to come prepared and ready to exceed expectations. There are benefits beyond just focusing on capturing a good picture. Make it a positive experience!