How long will it be until we uncover the 4 yr mystery?

From the wiki.

Shimmer One example of the denizens' love for freedom of expression is the unlawful synthesis of "Shimmer", a corrosive techmaturgical waste substance that is popular among Zaun's rebellious youth. When slathered onto the skin the Shimmer stimulates intense emotions in its subject. The Shimmer then creates an assortment of shining colors that corresponds to the emotion the subject is feeling. Though frequent application of the caustic glop can result in progressive degeneration of the skin and muscle tissue, a rumor that Shimmer can grant its wearer unnatural abilities has simply increased its demand.

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We know they both have sisters from in game VO - that Jinx line and a line Lyte the hermit has for VI in the howling abyss.

It's been speculated that they are sisters since Jinx was launched. No one will ever know the truth, is my guess.

i think it will just be one of those unofficially official things like how it never OUTRIGHT says aatrox is the one who slaughtered tryndameres tribe or that evelynn is the one who killed bruce vaynes parents

Found it.

We know from VO in game that each has a sister. Jinx: "You think I'm crazy? You should see my sister!" Lyte (Howling Abyss hermit) to Vi: "You look like your sister. Oh wait, I'm not supposed to talk about that."

which is enough to see they aint sisters. Their design's are polar opposites.

Certain champions seem to know both of them. Ekko seems to remember both and talks about events that are several years past, presumably. This has lead speculation that all three have been in the same gang at the same time. This is further fueled by each of them being associated with a Roman Numeral - VI for Vi, X for Jinx, and IX for Ekko (inscribed on the handle of his sword)

The gang stuff was a mistake on the wiki's part before ekko's release and was removed really quick, i see it's back on there now though. It still wouldn't make sense though. The roman numerals are a bit difficult to get anything from. Caitlyn's enemy is known as C. Other than that ekko got his by stealing a clock handle from piltover there's not much to go by.

We also have been told that both are orphans, that Vi apparently can't remember much of her childhood, and that Jinx wasn't always crazy.

Which leads me to believe Jinx did encounter Warwick as a small child. As i don't know exactly when Warwick was turned it could either be Post-Singed or Pre-singed warwick. Post-singed has a habit of losing control when he smells blood which could cause a small child some kinda trauma. Pre singed Warwick had just turned over a new leaf but had done something wrong.

As for vi, idk i'd like to think she just grew up in the slums of zaun without parents and ended up in a gang.

FYI: I believe someone from riot once said EVERY champion has a sister. maybe not anymore cuz we got a bunch of gods/spirits runnin around now.