*hugs* I'm sorry I don't have an answer, but here's my thoughts in no particular order:
1. Existing condition worsened by stress from the attack. Maybe a parasite like worms, mites/lice, coccidiosis. The gaping/vomit could in theory point to a gapeworm situation in particular if that...
No problem with questions! The crop is the organ where a chicken's food goes to be ground up for easier digestion. This article has a great diagram of where the crop is:
https://www.theselfsufficienthomeacre.com/2020/02/how-to-prevent-and-treat-sour-crop-and-impacted-crop-in-chickens.html...
Very sorry this is happening. I'm still learning, but if I suspect an illness/injury I try and do a full assessment. Are they eating and drinking normally? Can you isolate your sickly hens long enough to check their poop and take pictures? Do a crop check at bedtime for fullness, then check in...