I don’t know Russian, but maybe it’s possible to mistranslate siblings from sisters to brothers?
For some reason, many spanish speakers I know do mix up the pronouns and use ‘he’ when they should be using ‘she’, then vice versa.
At last, my one year of college Russian pays off! Sister in Russian is ‘sistra’ and brother is ‘brat’. So no, I don’t think it’s an error in translation. (The girls in my classes used to love the brother=brat).