The best lighting situation for an outdoor group portrait is during the "golden hour", which refers to the hour or so after sunrise or before sunset when the sun is low in the sky and the light is softer and warmer in color. This is because during this time, the sunlight is diffused and has a lower contrast, which can help to minimize harsh shadows and create a more flattering and even illumination across the group.
Additionally, it is best to position the group with the sun behind the photographer, which is known as shooting with "backlighting". This helps to prevent squinting and other unflattering facial expressions, and also helps to create a rim or halo effect around the edges of the group, which can help to separate them from the background and add depth to the image.
If shooting during other times of the day when the sun is higher in the sky, it may be necessary to use reflectors or diffusers to soften the light and minimize harsh shadows. Alternatively, shooting in a shaded area can also help to create a more even and flattering illumination.
Overall, the best lighting situation for an outdoor group portrait will depend on the specific conditions and preferences of the photographer, but shooting during the golden hour with backlighting is generally a good starting point.