#Emma: I hope it didn't hurt for them. I hope it wasn't scary. / Sonju: …

[fullscoreshenanigans]

First part is so so painfully canon with the nightmares we see from him in "The First Shot" bonus chapter:

The one child is being impaled through the chest as the nightmare demon grips him, which ends up being scarily similar to what actually happens to them. I also think it's cool how Demizu emphasizes not only the mouths given his focus of terror here, but down to the number of fingers he imagines them to have while working off his fragmentary memory of his year in headquarters

(Chapter 28 | Mystic Code Book Q&A Chapters 1 & 7)

When it seems safe to assume as Isabella's biological child he was frequently paraded in front of them as they kept tabs on his progress, so in his waking recollection he sees them more accurate to life.

Regarding gupna, based on this exchange in chapter 63, Ray knew about it before reaching Goldy Pond, even if he never performed it himself prior to that point.

There's also this panel of Emma teaching Don gupna at the beginning of chapter 59 and mentions of him performing it in the Don and Gilda short story in the fourth light novel:

So I think it's safe to say at least all the older Grace Field escapees who go hunting know about it before the end of January 2046 for practical purposes. Whether Emma or Norman ever talked about seeing the aftermath of gupna performed on a human with anyone else is up for debate, but Ray would be unaware of the specifics prior to escaping, so he was left to dwell on that as another facet of his failure for two and a half months, and we can see the toll it took on him during his speech in Grace Field's dining hall.

Just realized that before Ray escaped, he had no idea how demons killed the cattle children. like for all he knew he was watching as his siblings were shipped off to a brutal, gorey death. Imagine how much scarier his nightmares must have been, not knowing whether his siblings were being killed cruelly or not. The mind can be the scariest thing and no doubt he was imagining the most gruesome deaths and details. At least Emma and Norman had seen Conny and had an idea of how she was killed. But there was no way Ray was going to ask "was Conny's body like all torn up and mutilated or was she pretty much unharmed?"

When Norman was being shipped away, he still didn't know the details of what was happening to him. Not only was he losing his best friend, but he also didn't know if he was in for a painful and sadistic death or a quick one. He could’ve been picturing the worst and probably was. and when he escaped, at first his exposure to the demons was limited to the wild demons and the demons from Goldy Pond, both were trying to kill humans ruthlessly. it might’ve been a while before he learnt that the flower thing is kinda painless, it’s so sad to me