I'm not sure if you can mirror to other S4's. But what you can do is send your pictures or documents by bluetooth to those devices. If you do use bluthooth, make sure to name each device so you will know who your sending/receiving stuff from. Normally, when you receive something by bluetooth, it will have a notification in the notification bar. Just tap it and it opens the image. If you don't want to keep it, just delete it and your done. Hope this helps.
Correction: I just remembered, you can share contents on multiple S4's by using the Group Play app. You can share/play music, view pictures/videos, documents and play games. Not sure how many devices can be connected at one time though.