These are very often composites rather than a single wide-angle group shot. A common approach is to photograph each actor individually or in small groups, then cut them out and place them onto a photographed or generated background.

That avoids the perspective distortion you’d get from using a very wide lens close to a large group, and it makes spacing, pose selection, and scheduling much easier. Consistent lighting is the key so the final composite looks believable.

You can sometimes spot compositing in cast promos: mismatched foot angles on the floor, shadows that don’t quite make sense, or a lack of physical interaction between adjacent people.

That said, some large group portraits are photographed for real. In those cases, a common setup is broad, even studio lighting—often a butterfly-style arrangement with a large soft source above/near the camera—so everyone is lit similarly. To minimize distortion, you’d generally use a less extreme focal length and move the camera farther back rather than relying on an ultra-wide lens.

So the short answer: many TV cast promos are composites, but a true group shot is also possible with enough space, careful lighting, and a longer camera distance.