I suggest you look through this thread. Whether you decide to move them or not, it has some good ideas. If you leave them, please pay attention to the mark the eggs and check under the hen part. That could avoid problems.
I have seen a broody hen safely get chicks down from a 10' high hay loft. She said jump and they did. I would not expect a broody to have any real problems getting chicks down from a nest 3 or 4 feet high, but dealing with living animals, there is always a risk. It is also possible that a broody will fight you if you try to move them down and injure a chick that way. It is also possible if you move the hen before she is ready, that you leave behind good eggs that are late in hatching. I let the hen decide when she wants to come off the nest, but go whichever way you choose to go. I don't think there is one correct answer for this. I'm certainly not criticizing anybody whichever way they decide on this issue.
I let the broody raise the chicks with the flock. That way Mama takes care of the integration issues. She does not take care of pecking order issues for them since those are not in play until they mature enough to handle them by themselves and they have long since been weaned. I personally worry more about integration than pecking order issues, but there are risks with both.
Your having three broodies may complicate things. It is very possible that things will go well and you will not see any problems with that. Many people have several broodies together and never see problems. I'll mention a few things that might happen so you can be aware of the possibility and maybe help you decide which way to go. There is no guarantee that you will have any of these problems, but there is a possibility.
Sometimes a broody decides to take the eggs or especially chicks away from another broody. They fight over it. Chicks or eggs may get hurt in these fights. It is also possible that the broodies will work together as a team in raising the chicks.
Sometimes a broody (or even just another hen that is not broody) will kill chicks that hatch under a different broody. Some hens are better at protecting their chicks than others.
If the eggs are on a different schedule under the different broodies, a couple of problems can occur. Broodies will sometimes steal eggs from each other. Chickens can move eggs. I've had a hen move an egg from the floor to a nest about 18" high. I don't know how she did it, but that egg was in the ground in a tractor and was dirty. Later, that egg on the ground was gone and an egg with the same dirt marks was in the nest. That's why, if you have more than one broody, you need to mark the eggs differently so you know which eggs go with which broody. Otherwise, that egg can hatch early and the broody abandons perfectly good eggs in her nest.
Sometimes, when a broody hears other chicks hatching, she abandons her nest and goes to take care of the hatching chicks. Her good eggs are abandoned. Sometimes in these cases, the hens fight and sometimes they cooperate.
You asked if you need an area for each hen and her chicks. You can certainly do that or you can leave them together and see if they cooperate and work together. Maybe they'll take care of their own chicks and leave the others alone. If they are about the same age, yolu may be able to give all the chicks to one hen and break the others from being broody. You do not have to separate them from the rest of your flock. I don't. You have different options. I cannot tel you which is right for you.
I'll say it again to try to keep you from panicking. Many people have broodies together and never see any of these problems. But you are dealing with living animals and many different things can happen. This is not meant to scare you but to advise what might happen so you can be prepared, recognize it, and deal with it if it is a problem.
Good luck!
