If this said "nove filhos" I would translate it as nine children, suspecting that some of the filhos are really filhas. Does sobrinhos work in the same way, possibly including both sexes? . We can translate filhos as children, leaving the exact composition of the group unspecified, but English has no corresponding generic word for "nephews and/or nieces." How do translators handle this if they suspect that some of the "nephews" are nieces? Or, given that sobrinhos may include sobrinhas, then when it really does refer to the male sex alone, should we expect some additional wording to make that clear?
When you have a group, you should always use the masculine form:
- sobrinhos = nephews or nephews + niece(s)
Exception: avós = grandmothers or granfather(s) + grandmother(s)
So, if you say sobrinhos, you have to infer if they are only men or men + women.
To confirm they are only men, you can say "sobrinhos homens" ("male" nephews).