Welp, this is what Riot said about Ekko, Vi, Jinx.
From oldest to youngest, it goes Jinx, Vi, Ekko.
J.V.E come from different neighborhoods. If they were all from the same gang or neighborhood, it would make the world seem (tiny)
Ekko's knowledge of Vi and/or Jinx either stems from their renown or notoriety from when they were still in Zaun or purely because he crossed paths with them once or twice (especially Vi if he acquired a piltover clock hand as a weapon)
Also, if we ignore the idea of "shipping" and love (as much as I would love to have them together) the "I use to like a girl, til you started talking to the guns," could be taken as, "You know, when I first met you, like, 15 seconds ago, I didn't know you were uh...'eccentric'?"
The comment is probably geared to his random bid of disappointment or surprise when Jinx actually started talking to Fishbones.
Any comments towards Vi might be procced from him learning that she was in a gang, so he's just like "Why would you even bother with Piltover?"
But yeah. No idea who Jinx or Vi's respective sisters are (it is not each other, mind you).
No word or clue on who "C" is. The only thing people can go off other than the theory that Caitlyn is cray-cray and is her ultimate nemisis, C is from Zaun as the others are roman numerals.
Vi- VI -6
Jinx - X - 10
Ekko - XII - 12
"C" - 100
Something like that, but yeah.
