Nōnne iēiūnī erimus?

[Glūtinātor]

A sentence from paragraph 22 of Ora Maritima:

Nōnne iēiūnī erimus, sī nihil ante versperum gustābimus? (Won't we be hungry if we eat nothing before evening?)

I think iēiūnī is nominative masculine plural. If that's correct, is it because the speaker and the whole group making up the "we" of the sentence is male?

If the speaker and group were all female, would the sentence start, Nōnne iēiūnae erimus...

If it were a mixed group would it start Nōnne iēiūna erimus...

I know these are basic questions, but this text is pretty thin on explanation, I'm working alone and don't have anyone else to ask. Thanks for your help.

Glūtinātor

[bedwere]

Although some people today don't like that, a mixed group would be masculine.

[Serta]

To address your questions specifically, just expanding bedware's reply:

The group might be all male but could be mixed.
Yes, if all were female it would be ieiunae
No if the group were mixed it would be ieiuni

It's true that grammatical gender and biological gender sometimes don't overlap but the neuter is never used for something that is neither all-one nor all-the-other - as is common in many languages the masculine is the default.

[Barry Hofstetter]

Although some people today don't like that, a mixed group would be masculine.

Right, the masculine was the "common" gender when referring to mixed groups of people.