To tack on to what moose said, the total amount of "Warriors of Light" or Hydaelyn's choosen that we know of is 4. Us, Ysayle, Minfilia, and Krile. Basically, anyone with the Echo, whether or not they have risen up to the "prestige" of these 4 is unknown. I have my suspicions about Urianger, since he seems too close sometimes to issues related to echo users and primals in regards to tempering. There is also a debate on Thordan possibly being given the echo from Zodiark.