I think
Violet fits the "vibe" of the sibset.
Julia, while similar in some sense, still stands out to me a little.
I wouldn't worry about having a
Liliana and a
Violet as sisters. Does
Liliana get called
Lily a lot? Would you use a nickname for
Violet?
Vi / Vee etc? I think I'd be more concerned about using EmiLIA and JuLIA in the same sibset. But that's just my opinion :)