Process and Documents required for S1 visa extension for my wife and son

You can extend their residence permits instead of S1 type. First, you need to provide their passport, photo, application form, residence permit, medical examination report as well as your relationship certificate and others. And then go to the exit and entry administration of the local PSB to make the extension. Just for reference. If you still have doubts, you can contact the local PSB to inquire details.