
My favorite piece of fanart for the entire Final Fantasy series. It's just so... warm.
I could have sworn the game said they were sisters when I was playing it, then I was reading online and realized they weren't sisters and I was like, "Oh wait a minute..." 
They do share part of their names, which can be easily be confused for having the same family name, but is actually a demonym, referring to their birthplace of Oerba.
Even the original suffered from a lack of realistic human drama in comparison to the fantastical nonsense and made up terminology. The characters just act weird, and it's hard to understand how they're feeling when their struggles have so little basis in reality. 
Couldn't agree more. FF13 has frustrated me to insane levels because it had ALL the prerequisites for writing good drama in fantastic context (my favorite thing in fiction), yet squandered all of them so meticulously, as if the writers were doing it on purpose. To boot: Lightning is a woman who got too much responsibility too soon in life, and estranged herself from her beloved sister because she thought she knew better what was good for Serah; Sazh is a single father coping with the fact that his son was taken from him by the government for something neither of them had any control over (isn't it any parent's worst nightmare?); Snow is an idealistic, if insecure idiot with too much energy and charisma who has the understanding that reality doesn't just magically turn out the way he wants painfully beaten into him; Hope is a boy coping with the death of his irresponsible, but loving mother by bonding with a woman who has clearly proven herself to be an utterly incapable mother figure; and Vanille has a massive guilt complex for what happened to Sazh's son when she and Fang awoke, and much more for holding Fang back during their first attack on Cocoon, and thus failing their mission and ensuring the extinction of their native civilization. Fang, in fact, seems to be the only main character who has clear goals and very little drama in her life, which actually serves as a nice counterbalance to the other five.