Okay if I were to write Parallels, here's just a brief look at the personality of each Twilight.
Twilight: Regular Twi.
Nightlight: She is from the universe where Nightmare moon took over and is really shy and has no self confidence because of this oppressive sad world. She never met the mane six nor did Spike meet Rarity four years ago so there is Spilight in this universe.
(Insert clever Twi name here): The final Twilight is from the future universe that's 700 years ahead of Equestria. She's pretty much a badass who acts a lot like Rainbow Dash. She has a lot of future guns and future tech and makes fun of the other Twilight's for being so stoneage. Also in her universe Rainbow Dash is a bookworm, and princess Luna and Celestia are either Premiers or Prime Ministers. Also Equestria is a democratic republic. (The Allied Republic of Equestria)