"Were they victims?"
Translation:Ĉu ili estis viktimoj?
I think in that context "victims" is an adjective, or it needs a preposition instead "Where they THE victims?" (victims is now a substantive) or instead "where they victims?" I understand victims is now an adjective, therefore "ĉu ili estis viktimaj?" should be the right answer.
I think it is a noun in the English sentence (and also should be in the Esperanto) I tried imagining what it was in Norwegian and in the totally similar sentence it was a noun. Ĉu ili estis viktimoj is a less ambiguous and thus arguably better sentence than
Ĉu ili estis viktimaj
viktimaj ranoj? viktimaj policanoj?
I think both are right, and it is ambiguous because I can ask you, who are the victims and were they victims referring as a noun. But I also can ask you if they were victims, being victim the status of a crime scene:
Are they green? Are they victims?
"Are they cows?" In this sentence, cows is still a noun, not an adjective.
The verb "to be" isn't exclusively used with adjectives in English, it can also be used with nouns.