Hello ! Why "jsou bez nas a jsme bez nich" is not accepted please ?
You put they and us into a contrast, you can't omit them.
Why was "Oni jsou bez nás a jsme bez nich" not accepted? I thought the "my" was for emphasis or to make it easier but not strictly needed?
See Vlada's answer above.
So as "stand alone" phrases, neither of these would need a pronoun. But since they are being compared to each other in the same sentence, pronouns are needed? Safe bet that it's pretty much always the case in comparison sentences?
They are without us, and we are without them. I missed a comma in the answer, it was not accepted as the correct answer. Really?
Commas, as all other punctuation, are ignored by Duolingo. Use the report button next time.