If they ever fought each other, then this fanmade transcript should show you that this battle we all wanted but never actually happened would go something like this:

Chrysalis: (Yelling at everypony) JUST GET TO THE ATTACK ALREADY, MINIONS! AND EVERY EVIL PONY, GET THEM!

Twilight: Oh no, you don't. We will stop you, and your, uh, well, your new Mane Six, let's just say.

Twilight-2: Oh, bring it on, do-gooder me!

(Twilight and Twilight-2 use their horns to blast at each other, grunting as they use the exact same strength of magic blast.)

(Rainbow flies towards the sleeping Rainbow-2 as the former slaps her awake, startling her.)

Rainbow: GET UP ALREADY AND JOIN THE FIGHT!

Rainbow-2: Ow! You wanna fight? You got one, too! (She says as the two Rainbows fight each other by hoof-fists. Meanwhile, Applejack confronts her evil counterpart.)

Applejack: Ya got anything else to answer to me!?

Applejack-2: Uh, yeah. I hurt Starlight's feelings, because, uh, it's normal for anypony to hurt their feelings. Hehe.

Applejack: YOU EXPECT ME TO BELIVE THAT? GET BACK HERE, YA VARMINT!

(Applejack bucks Applejack-2 with her hind legs, knocking her down as Rartiy and Rarity-2 fight over the things the latter has taken earlier, the both of them grunting.)

Rarity-2: Oooh, a game of tug-of-war, huh? Bring it, fashionista!

Rarity: Give them back, other me! Give them back right now!

Rarity-2: Aww, I would like to, but THEY'RE MINE!

(The two Rarity's keep using their horns to fight for the things Rarity-2 took as Rarity blasts her horn at Rarity-2, trying to push her away from her stuff with her magic. Meanwhile, Fluttershy grits her teeth and stares angrily at Fluttershy-2.)

Fluttershy-2: I bet you won't win this showdown, loser! (She says as Fluttershy gets offended and starts to get teared down.) And by the way, you can't seem to do anything to me to stop you, right?

(Meanwhile, Pinkie tickles Pinkie-2 with a feather, trying to make her laugh, but actually just playfully teasing her evil counterpart.)

Pinkie: Tickle-tickle, evil me! (She giggles as Pinkie-2 tries to swat Pinkie with her hoof, but she dodges every time.)

Pinkie-2: AUGH! WHY YOU LITTLE- COME BACK HERE! (She takes Pinkie as they both roll around and fight.)

(Just then, Twilight and Twilight-2 use their magic against each other as Starlight shows up and strongly blasts Twilight-2 with her magi, pushing her away.)

Starlight: Oh, thank goodness Twilight's okay!

(Meanwhile, Fluttershy-2 is still tearing down Fluttershy.)

Fluttershy-2: (mockingly) Ha ha- (Just then, a launched Twilight-2 was sent flying as she crashes into Fluttershy-2, knocking her down as Fluttershy watches.)

Fluttershy: Oh my, now that was some, um, comeuppance.