That's completely understandable. I have some that I wasn't able to bring myself to look at either.I do not think I could bring myself to do a necropsy, even with my medical background.
I am so sorry you lost your birds, did you figure out what happened?
I do let my big girls "free range" under supervision for about an hour a day. Have done so since they were about 3-4 months of age. I stay out with them and clean the coop and do other chicken chores, as we have daytime predators here. I suspect she may have ingested something, no way to know if it was something poisonous. They do not go off of our property and we do not use any pesticides of chemicals on the property.
We're pretty sure they got into the neighbors "compost". They usually go and dig through the horse poop there, and mama was constantly bringing her chicks and 2 other birds with her to check out the compost. Mama survived, 3 (one was the last to show symptoms and we fibally knew what to warch for and immediately brought her inside to monitor) of the little ones survived and the 2 other birds died from other causes (freezing and a broken neck). But she lost around 4 babies. All 6 that didn't make it had abscesses* only on their liver, nothing else and the young ones all died from their livers failing.
We did check into about 20 different diseases that matched one symptom or another, but none of them marched more than 2 at most and all had other things that weren't present on the birds.
We know the neighbors throw trash ash on their compost and im certain the birds are some of that ash while there.