A likely setup is a large overhead scrim or diffusion panel to block direct sun and soften the light across the whole group. That would create broad, even illumination while still leaving some gentle shadows, which matches the look described.

The front of the group may also have been lifted with a large reflector/polyboard, or even by light naturally bouncing from pale ground or nearby stone surfaces. That can give a polished, bright result without looking like obvious artificial lighting.

One answer noted the catchlights and shiny reflections didn’t strongly suggest a small hard light source, so flash may not have been the main light. However, after seeing the original image, a small amount of front fill flash was considered possible.

So the most plausible explanation is: diffused daylight from above, plus frontal fill from a reflector and possibly a little flash. That combination can make an outdoor portrait look very controlled and “studio-like” without any green screen or compositing.