"Our parents help you all."
Translation:Unsere Eltern helfen euch.
As a plural 'you', euch already contains the 'all' part of 'you all'. You can explicitely add 'all' to the translation, but in this case it would be allen, and not alles which means 'everything':
"Unsere Eltern helfen euch allen" should be an accepted translation.
Should be but isn't! I have just had it re4jected. "You all" is an Americanism, but so long as it is there, you should translate it.
"You all" is indeed an Americanism, though not used by the majority. I would use "all of you" rather than "you all"
Seems that Duolingo is doing some tricks to inform us about “ihr” and “du”. I see a lot of “you guys” for the plural “you” in the Chinese course.
What if you want to be formal? I interchange euch with Sie and DL rejects it!
“Helfen” takes the dative. If you want to be formal, it should be “unsere Eltern helfen Ihnen”, and that's likely to be already an accepted translation.
Yes, but it doesn't sound like standard word order to me. Unless you know what you're doing with how it affects the emphasis, stick to the phrasing suggested by Duo.
It's not strictly necessary to add all(en) to the German sentence. You just need to use one of the plural forms of "you" (in dative case), i.e. euch or Ihnen.