when is an interview required for S1 visas?

i have an executive moving to China to work. I am getting his Z type and I know he has to go to Washington DC in person to receive that. His wife and children need S1 types, but I can't find anywhere if THEY are required to go the Embassy in person as well, or if they can just apply for those through a visa agent here in Utah.
Desperate for clarity on this situation. Thanks!