Historically correct: כְּלָבֵ֫ינוּ [kla've(y)nu] our dogs; colloquially possible: כַּלְבֵּ֫ינוּ [kal'be(y)ny). You put the light suffixes on the plural stem כְּלָבִים, only the heavy suffixes on the construct stem, i.e. כַּלְבֵיהֶם [kalve(y)'hem] their dogs (notice the [v]!).
It means they're running and just happen to be outside. If you want to imply movement into/out of a place, you should use פנימה/החוצה. Here are some examples:
אני יוצא החוצה - I'm going outside
הם משחקים כדורגל בחוץ - They are playing football outside
הכלבים רצו פנימה - The dogs ran inside (into a place)
החלטתם להישאר בפנים - You decided to stay inside (/indoors)
Yes I got that from the tips and notes, but it's also stated there that both "כלבנו" and "כלבינו" would be pronounced "kalbenu". But from the audio sample attached to this phrase it's pronounced as "kalbeinu". So I just wondered if that's a real difference in the pronunciation that is made because it's the plural version or if it's just a dialectal variation?
That makes sense, but "antonsamuel" should know that Duo IS making a distinction in the audio so that you can know if it's plural or singular (כלבינו vs כלבנו). I don't know how it's spoken in Israel, I guess it could be that they just infer if it's singular or plural from the context... but there definitely is in theory a difference, and honestly I wouldn't have thought it's based on dialect.
Well, yes, the colloquial plural כַּלְבֵּ֫ינוּ [kal'beynu] our dogs is based on כַּלְבֵּ֫נוּ [kal'benu] our dog. Most nouns use the same stem (סוּסֵ֫נוּ [su'senu] our horse versus סוּסֵ֫ינוּ [su'seynu] our horses) and this is generalised for nouns who actually should have a different stem for the plural. And not everybody makes the difference between [-'enu] and [-'eynu], which was originally only an orthographic differenciation, so סוּסֵ֫נוּ and סוּסֵ֫ינוּ can indeed result in the same pronunciation.