Yes, thank you for this. It really does seem like they're asking for the original for some reason and not a copy, otherwise it would say "a copy of a passport" surely right? It's so confusing to me, and I forgot to put that question specifically in the original post. Thank you for picking up on that by the way!
But yeah this is stressful. So far we've taken scans of every page of both our passports and scans of both our birth certificates too (as like an extra thing just in case).
Seems like they wanted all pages of the passport all along and not just the birth certificate, so that's interesting, definitely something to think about for others in future!
I wonder if we can like contact USCIS in some way (maybe using the live chat or something?) to ask for clarification because we're worried about getting this wrong and getting denied.
It's just so strange to me it's vague enough that it doesn't say "please send us your original passport" or "please send us a copy of your passport", because you're right, literally it sounds like it's saying it wants both of our actual, physical passports.