Yesterday I put 12 eggs under two chickens. I started out with 12 eggs under one chicken but she's not big enough for that many eggs so the little silver 41 week old chicken that's broody got half of them.
Today, the older hen got 2 added back to her stack, and the little one got set back onto the 4 oldest eggs. I doubt the young one stays with it and I also doubt the oldest eggs will be viable anyway, they usually aren't, which is why she has eggs 1-4.