That's only if you really want to overkill the stress on the fact that there are both women and men (or boys and girls, etc.) in the group. I'd not use it for mixed group myself, only when there are 2 groups, one of consisting men, and one consisting of women. Otheriwse it would sound odd.
I have similar in my language (one/oni) and I understand that this can be confusing esspecially for someone whose native language is English. I think that it would be better if the author of the questiond would wrote to translate to Polish "They (females)" or "They (men or mixed group)". This way when it says translate you can put both and it will be correct answer and one will still be confused.