My suggestion is that you break one of those hens from being broody. If you can elevate a cage with a wire bottom so air blows up under her, keep her in there for three or four days with food and water but no place that looks like a nest, she will usually break from being broody. If it doesn’t work, just do it again. This will be a lot less disruptive than trying to integrate new chickens. And you have quarantine to consider.
Many people have multiple broodies that work together to hatch eggs and raise the chicks together or that have their own nests and eggs and hatch and raise them separately but sharing the same coop and run. Sometimes though you have problems. The two broody hens may fight over the eggs or chicks. I had that happen once, when the eggs under the first broody started internal pip and starting chirping inside the egg, the second broody attacked to try to take over the nest. Half the eggs were destroyed. Sometimes one broody hen will kill the chicks under the other broody. I haven’t had that happen but several people on this forum have reported that.
I cannot guarantee that you will have problems, you may not. But I think your best way forward is to break one of those broody hens and let her other take care of all the eggs and chicks.
