Translation:Do they trust us?
The chaH is not necessary. The sentence would mean the same thing without it. I suppose that without the chaH it could also refer to animals or a singular bring capable of language, but with the chaH it makes it clear that it is referring to multiple beings capable of language. None the less, using the pronoun in a sentence like this is completely optional. Some of our sentences have a redundant pronoun and some of them don't.