I think, it is their official name in japanese..in anime, Law referred them as Tobi Roppo

If I am not wrong Tobi is from tobu mean Jump/Fly..and Roppo mean Movement in Six Direction..well it is pretty much The Flying Six

And Actually tobi roppo is a popular style of walk in Kabuki Theater..

to think that their first shoot of appearing was their walking feet, it is just amazingly perfect..

I believe so you can definitely see X Drake in the bunch

Yes he is