It's a bit murky. As far as I know, it's not explicitly addressed in the film or written materials, and the closest is this quote from an [Entertainment Weekly write-up of an interview with Abrams](http://www.ew.com/article/2015/08/12/star-wars-force-awakens-kylo-ren/2):

> Remember how we eventually learned that “Darth” is not a first name, but a kind of title? It appears the surname “Ren” is something similar.
> 
> “He is a character who came to the name Kylo Ren when he joined a group called the Knights of Ren,” Abrams says. But that’s as far as the writer-director will go.

*(Note: this interview was before film came out- I'm not aware of anything more recent on this)*

This is being interpreted as a sign that other Knights will have names like "Brian Ren" and not names like "Kylo Stimpy", for example in this quote from [cinema blend](http://www.cinemablend.com/m/new/Luke-Skywalker-Isn-t-Kylo-Ren-Right-89247.html) which I found in this [answer to a similar question](http://scifi.stackexchange.com/a/111283/31938) about whether his name is based on other characters' names:

> As we learned in an interview with Abrams in Entertainment Weekly, "Ren" is the title, which refers to a mysterious organization called The Knights of Ren. "Kylo" is the unique signifier, a name Kylo Ren chose for himself for some equally mysterious reason

But they might be over-interpreting EW's over-interpretation of a vague statement. Unhelpfully, Cinema Blend don't link to or reference which EW interview or write-up they're referring to, but I can't find one that comes any closer to a confirmation than the one I quoted from.