Sooo, i will change some canon things muahahaha. I never liked the whole highschool thing of Equestria Girls, since i see the mane 6 as 20 years olds in the show. Instead, Canterlot High is now Canterlot College. And spike doesn't turn into a dog and thank you kiwigoat-art for helping me with your suggestions!!

1) After being sent to the alternate Equestria 1000+ years ago, the sirens kept singing, waiting for a spark of equestrian magic. They have been through it all, they have seen it all. In the present times, they are Pop Stars, the Dazzlings, they love the fame, but they loved causing chaos more. After they felt what Twilight magic did to Sunset Shimmer when they were in the town for their tour, they knew they had to go there. Since Twilight couldn't help Sunset, they charged enough of their powers and went to the real Equestria, Sunset following them. Of course, they teamed up with Nightmare Moon.

2) The "pony" form of the Sirens, it's more comfortable than their real form~