So far, so wonderful.
There are a few grammatical errors here and there, and that odd thing going on with the quotation marks, but nothing that really diminishes the story. The only thing I would question is near the end there. Why would Twilight & Co. believe Luna, exactly? She still didn't offer any definitive proof, only a loud-speaking voice that puts a great strain on Luna when she uses it, and some pieces of information from this supposed "alternate world" without any way to back these claims up. For all they know, it could be a ruse. According to the Ponyvillagers, the Luna of this world is supposed to be the "The Tyrant Sun's Puppet".

6379046 Only ponies that are worthy can use the Royal Canterlot Voice. And Lunar is about the furthest away from being worthy (with the exception of her sister of course).

6380134

Alright. I take it then these Malicious 6 know this as well? I might have missed that part.

6379046
That is true, but Lunar is not capable of using the Royal Canterlot Voice. Therefor Luna did it despite it hurting her. Also Twi and her friends have realized something odd about her behaivour.
And about the grammars and quotation marks: German Libre Office, thank you very much.

6380134
Good explanation and yup Lunar can not use it. Just like Celestiar. They never used it and therefor their vocal cords are too soft to produce such a thundering call.