Tali ftw, btw.
Regarding Sak and the rest of the girlie horde? No distinct influences, at least in terms of personality - as I've said elsewhere, I'm a fan of strong women, especially the types that strike the right balance between strength and femininity. So when I see anyone in RL, games, TV, etc. that strikes me as having the right kind of attitude, I keep them in mind if possible use for the influence comes up.
Some examples I can think of for each of the sisters, off the top of my head, range from:
Sakura - Motoko Kusanagi (Ghost in the Shell)
Akusa - Andromeda (Gene Rodenberry's Andromeda)
Ereka - Samantha Carter (SG-1)
Eri - Kaname Chidori (Full Metal Panic!)
Ami - Asuka Langley Soryu (Evangelion)