That's great news!I was able to rehome the four older babies.
I do not know for sure if that is what happened or not.I also think the one that died might have been attacked by the older ones. This is a picture of the dead baby. It has a weird bald spot on it making me think the older babies ripped it’s fur out.
But if you had removed the older ones when the new litter was born, there would have been no chance for them to hurt a younger one. (It might have died anyway, if the older bunnies did not cause the death, but you would not be wondering whether or not they had done it.)