The usual fixes are to add fill light or redirect existing light.

For smaller groups or portraits, a reflector is a strong option: place it to bounce sunlight back into the faces and lift the shadows. A collapsible reflector works well, but any large bright surface can help if positioned correctly.

For more mobility, fill flash is often preferred. It lets you work without extra stands or assistants, and can brighten facial shadows effectively. A ring flash or ring-flash adapter can be especially useful for fill because the light is centered around the lens and tends to fill shadows more evenly.

For larger groups at greater distances, both flash and reflectors become less practical because neither reaches very effectively unless the light source or reflector is very large. In that case, the best solution is usually to change the conditions rather than force it: move the group into open shade, turn them so the light is more flattering, or shoot at a different time of day when the sun is lower and less harsh.