Gist
Yes. The wide stance can increase glute contribution, but stance width alone does not replace progressive resistance and adequate depth.
They train the core to stabilise the trunk over a wide base, though the movement is still primarily a lower-body exercise.
The calves help stabilise the feet and ankles, but the wide stance does not turn the squat into a strong calf-building exercise.
The hamstrings contribute to hip control, yet sumo squats are still a secondary hamstring exercise rather than a substitute for hinges and curls.
Yes. The quads still extend the knees in a wide-stance squat, although an extremely wide stance can change the balance of work toward the hips.