What F-Stop Should Be Used for Group Shots
When you're choosing an f-stop for a group photo, there are 3 factors that will influence your choice. The first is that you're going to need lighting: the more open your aperture is, the grainier the image will be and quality will be lost. The second factor is the size of your group and the location of the shoot. A large group means you will need a lot of light to cover anyone, and your location could help or hurt this depending how much natural light comes into it. The last factor is how powerful your lights can be.
F/stop for Group Shots
Ideally you want something above an f/4. This will keep your image looking sharp. However, you can't always get that because your lights and the size of the group can make it so your powerful lights are farther away then you'd like and intensity is lost. Remember that in a group photo the lighting is flat and even. You have to keep that lighting strategy. One side of the group darker than the other is unacceptable.
So the answer to what f-stop to use for a group shot is whatever keeps the aperture closed the most while keeping your lighting even.