"Does the man trust them?"
Translation:An bhfuil muinín ag an bhfear astu?
In English you can "trust somebody" but you can also put "your trust in somebody", where trust is like a singular noun. It's a thing you have. Tá muinín agat. So, "does the man trust..." is "an bhfuil muinín ag an bhfear...". Then it's "out of" the subject, so 'asam, asat, as, aisti' etc. http://www.daltai.com/grammar/prepositional-pronouns/