is that really Anastasha or is it another girl named anastasha who is acting like her

In the film, because it is fictional, yes, it is Anastasia, but in real life, there were many impersonators but none of them were truly her.

Well in the cartoon version she suffered from amenisa and 10 years later she is living in an orphange. Of course she goes by the name Anya but she has no memories of her past until she decides to go to Paris along with 2 con men Dimtri & Vladmir.So to answer your question yes she did exist.

No, it's not. It's just some other girl.

There was suspicion on whether or not she survived the attack of the Bolshevik secret police in 1918 (which is what really happened, not the Fox Animation Studios version of the story), but her body was discovered in 2007. They ran tests on it, and it was confirmed in 2009 that it was indeed her body. No one escaped the attack.

Its someone acting as her. Anastasia was killed in the Russian Revolution, and though some people say she survived she didn't really, its just a myth.

Even if she did survive, the Russian Revoltion was over 90 years ago and she would almost certainly be dead by now, or too old to play a young girl, anyway.

Hope that answers your question! :)