Translation:You are walking
Second translation provided here is "you all are walking". That's a strange word order for English. Surely the translation is really "you are all walking"? Whilst in some situations we are likely to say "you are walking", sometimes it is necessary to be precise about the people walking, making the second translation necessary in English.
Yeah, the "you all" only really works for English dialects (Southern US mostly) that use it to indicate plural "you" (usually contracted to y'all). You all are is basically just you [plural] are (in these dialects), but you are all stresses that it's the entirety of the group, and in Swahili, that would be: (Ninyi) nyote mnatembea.