Who are the Knights of Ren? Are they force-sensitive? Where did they come from? The Visual Dictionaries, Secrets of the Sith, and the comic book The Rise Of Kylo Ren give us that answer.
A little extra bit of information that I didn't cover in the video (because I forgot); the Knights Of Ren seemed to know who Snoke was in the comic book, hinting that they were doing his bidding at some point. That may explain Snoke's line in The Force Awakens about having multiple apprentices.
