Creo que es una pregunta sobre la gramática inglesa, ¿verdad?
In this case, 'are' is correct because you're referring to 'women' and 'men', which are plural nouns:
- Half of my [group of ] friends are women, the other half are men.
Similarly, you can't refer to 'half the group' as 'it':
- Half of them are women.
In other situations, you can use either a singular or plural verb conjugation because there's no obvious singular or plural noun:
- Half the group is/are ready to leave.
- Half of them are ready to leave.
... because 'them' is clearly a plural subject.
Por cierto, ¿cómo se dice en español? "La mitad del grupo es/son mujeres"