i don’t think ren is a title, i think it’s just a new name he came up with.
The implication I got was that all of the Knights of Ren held that same title. But I don’t believe it’s been confirmed either way yet.
the implication i got was that the knights of ren were kylo’s knights. like, it’d be the same of there were the knights of vader. they’d be vader’s knights. something like that.