Misha is older by around five minutes. They're of Russian/German/English ancestry. Both fluent in Russian and German, Misha's English is much better than Marya's through the wonders of the internet he just chooses to not talk lol.
Mikhail Dmitrievich Kossakovsky ---- Misha (Миша)
Marya Dmitrievna Kossakovskaya -- Masha (Маша).