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Umm, Irina sounds similar, but the origin of Erin is gaelic (I looked it up), and that of Irina is Greek. I don't think there are any Russian names that come from Ireland. Basically, Irina is Irene.

That would be Nicolai or Kolya, respectively; both are male names

Николай, Коля

I can't think of a Russian version for your name, but if you were to write it in Russian letters, it would look something like this

Эрин