Well, obviously these are very dignified beings in a situation that demands our delicacy and respect, so let’s ask, thusly:
Önök mit csinálnak itt?
“Sirs, what are you doing here?”
The English translation leaves a lot to be desired. Hungarian doesn’t have a gender. I don’t know what to use in English for a gender-neutral “sirs.” Also, the English translation is a bit ambiguous – what are you doing here has two possible senses, one of which is why are you here, which is not the sense of this sentence. This sentence is asking for a description of the activity that is taking place.
Notice the polite conjugation of the verb “csinál,” as appropriate to the formal address.
Mit is the object. It is vague enough to be considered an indefinite object.