A lot of people are confused thinking that the Knights of Ren are all force users/sith/former jedi. But the only one actually wielding a lightsaber is kylo. I hope this thread gets seen by more people.
I don't know about that. We don't have enough information to know who or what they are yet.
The lack of lightsabers doesn't necessarily mean they aren't former Jedi or force sensitive. We see a Jedi who isn't wielding a lightsaber in this scene.
The only new lightsaber we see looks like it's pretty poorly made. This could mean the knowledge how to build one has been lost. This is unlikely since, traditionally, young padawans were taught how to build lightsabers and Kylo was probably 20 when he turned, and there were adults and possible full fledged Jedi when certain tragic things happened. Not to mention Snoke, who is supposedly very old and very experienced, really should have some knowledge how to build a lightsaber whether he's a Sith or not.
Also Kylo's saber is modeled after a style that was popular in the KOTOR / Revan era, so some knowledge of lightsabers exists. So information how to build one is probably around, though the type of training and guidance needed to perfect one is probably pretty rare.
According to the Visual Dictionary, one of the reasons for the unstable blade was Kylo's cracked Kyber crystal. I imagine if he had access to a better one he'd probably get one. That makes me think the specific type of force-tuned Kyber crystals are probably rare now.
All of this is supposition and we don't have any real information to go by here at all. Though there is a lot of concept art of the Knights with lightsabers and swords and blasters too.
