Translation:Father and also mother are in the city.
It might be a mistake. As far as I know, 'quoque' follows the word it refers to. So it would be more like "Father also and mother are in the city". It would point to 'pater' and not 'mater'. If it's some kind of exception, I guess someone with more experience with Latin could explain the logic behind the structure.
In my Latin reading experience, quoque is postpositive. Thus pater quoque et mater would be "the father also, and the mother" (a bit nonsensical) or "The father and mother also are in the city," i.e. "also the father and mother . . ." (if the previous sentence mentioned a third person being in the city). However, for the translation given, I would expect to see: Pater et mater quoque in urbe sunt. Am I missing a certain usage?
English is not Latin, but I found a few examples from early ModE in the AV of the Bible that are suggestive of this Latin sentence, where also appears to modify the second conjunct:
Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field; (Genesis 3:18)
Unto Adam also and to his wife did the Lord God make coats of skins, and clothed them. (Genesis 3:21)
I wonder if those might somehow be gramnatical or stylistic reflections on Classical Latin (and Ancient Greek).
Certainly Greek uses και and δε in this way. Consider 1 John 1:3 και η κοινωνια δε η ημετερα "And our fellowship also is . . ." The trouble is that I don't recall coming across this construction in my Latin reading (which is admittedly limited to Caesar, Vergil, and Augustine), so I would rule out Latin influence on English. (The Vulgate of 1 John 1:3 doesn't even translate και. Apparently even Jerome found the construction awkward in Latin.) Although there is no reason why one couldn't say "the father also, and the mother" in Latin, the Duolingo sentence has no context to support such an unusual construction. As for the AV of Genesis, on the face of it, the AV translation seems like an effort to avoid too many "and"s without simply leaving one "and" untranslated (like all the modern English versions do). I guess that it just sounds bad to the English ear to say "And thorns and thistles shall it bring forth . . ." (וקוץ ודרדר תצמיח). Again, Jerome only translates one of the two conjunctions in Genesis 3:18, rejecting the Hebrew polysyndeton as awkward to express Latin. Jerome varies the conjunctions in Genesis 3:21 by using both quoque and et for the simple Hebrew waw, but the conjunctions are several words apart, unlike the Duolingo example in question.
That doesn't work since "quoque" appears to be modifying "pater" only and not "pater et mater." (... But then again Duo's translation has "also" modifying "the mother" instead. As you can see from the other comments on this page, the sentence seems like it may have been poorly written or poorly translated.)
Thank you. I can see how it could be as you suggested and that is obviously what the course designers had in mind but I flagged it anyway so at least maybe they'll take a look at it and see where it could be a confusing sentence. All that said I really am happy with the course content and blown away by the level of knowledge of Latin that some of the people here have.