Simultaneously looking after chick and brooding 6 eggs

[Lids]

I feel I am experiencing something unique.
I bought 5 broiler day old chicks. I put them with a mama with 4-day-old chicks, since they were about the same size. Specks, my Boschvelder hen instantly accepted them as did her little chicks. But when she started assessing them, she saw that they weren't up to the level of her chicks and a real liability. Our chickens walk free and there are many predators, like raptors, monkeys and monitor lizards. So she started culling them. I managed to rescue one, the littlest.

I also have a mama who had been sitting on eggs for only 4 days. (17 to go, which is a looong time.) I put Horalce with her. She accepted him immediately. Every day I think she might abandon her nest, but every day she surprises me. It is now day 12 and she has a week to go till hatch. She will have a 17-day-old giant when her other six are hatching!
Specks went to visit Ms.Marple and tried to get her to leave the nest, or to entice Horalce to join her. But he loves his mama. And Ms. M knows her eggs are viable and just need more time.

Has anybody experienced a similar thing?

I will try to keep you all updated. I am monitoring things very closely.

Update: Hatching went smoothly yesterday, but suddenly Horalce (who turned out to be a girl!) became fidgety and enticed mama to get up and go and to bring the kids. Shame, they had just hatched, were still dazed and wobbly and hadn't yet learnt about being quick and quiet. She started to peck at them so I removed them and put them with another broody--a first time mum.
Seems like this whole thing started a major relay...
I am very impressed with the broiler chick's intelligence and maturity. She started exhibiting mother behaviour, like warning before she stretched or fluffed, and calling the chicks to eat. She eats voraciously and is constantly thirsty, so I am wondering if it will be reasonable for her to be scavenging outside like my other hardy Boschvelders?