I was doing the audio exercise: is the "m" in "bebem água" silent in Portuguese? I know French has a lot of silent letters, especially at the end of words, so it seems entirely plausible, but it could also be a quirk of Duo's text to speech.
It's not silent but it's kind of nasal. So you don't come to a hard stop at the end of the word
It's more common in Portugal, but yes, you can always use the article for emphasis.
So does the possessive pronoun here have to agree with the gender of the subject it modifies or with the person/people speaking? If we are all male and the cats are female, would "Nossos gatas..." be correct?
It agrees with the subject it modifies (Nossas gatas); the only cases where it agrees with the possessor are "dele/dela/deles/delas" (his/her/their - masc./their - fem.)
How do you distinguish between the present simple and the present continuous form?
BP uses estar + gerund to make a sentence progressive in the present:
- Nossas gatas não comem. Our cats don't eat.
- Nossas gatas não estão comendo. Our cats aren't eating [i.e. right now].
I believe, "are [not] eating" is actually a present participle rather than a gerund (which is a verb masquerading as a noun).