Thank you, bcr229, for your response. The hatchlings stayed in the eggs for another 3–4 days. There was no tangled umbilical cord. Two of the hatchlings were already dead when the eggs were cut open — as if they were too weak and couldn't manage to cut through. The inside of the egg was scratched, but there wasn't a single clean cut. Two of them, despite having unabsorbed yolk sacs, have rather large bellies — it doesn’t look like hard belly for now — and two are quite skinny. I'm still trying to figure out where something might have gone wrong.