There are no common practices. For thousands of years broody hens have been hatching and raising chicks with the flock. For thousands of years people such as the ancient Egyptians have been incubating eggs and brooding the chicks themselves. I don’t know when people started isolating broody hens from the flock when they were incubating and brooding chicks, but I imagine is started about the time chickens were domesticated. There are benefits and risks no matter which way you go about it. It’s not that one way is right for everyone and all other ways are wrong, it’s which you choose to do. Since we are all unique in our goals and set-ups, one way might be better for some than others.
I let my broody hens hatch the eggs in a common flock nest. I mark the eggs I want her to hatch with a black Sharpie and start them all at the same time so I don’t get a staggered hatch. I check under her every day after the other hens have laid and remove any eggs that don’t belong. Others isolate their hens when incubating.
When my hens hatch, I let the broody hen decide when to bring the chicks off the nest. Before the eggs hatch but after the chick internal pips, it starts talking to Mama so she knows when more are coming. She knows more about that than I do so I leave it up to her. I’ve seen a hen get her chicks down from a 10 feet high hay loft, Mama says jump and they do. Then they bounce up and run to her. It doesn’t bother me if a nest is a few feet off of the coop floor. That really bothers some people.
I once let a hen hatch in a cat litter bucket with a top 7-1/2” X 11-1/2”. That was too small. The first chicks to hatch often climb on top of Mama to pass the time. If the nest is too small like that one they miss the nest and fall all the way to the floor. Four different times I tossed chicks off the floor and back in the nest with Mama. After that hatch I retired that nest. Just an example of how your facilities can make a difference.
If the coop is not pretty full, I put food and water on the coop floor where the chicks can get to it and leave everything else up to Mama. She takes them out of the coop when she’s ready and raises them from that point forward. I have a big area in electric netting so she has plenty of room.
If the coop is pretty full, after she brings them off the nest I put them and her in a coop on the ground out in my run and leave them locked in for a couple of days. After that I turn them loose to roam with the flock. Mama will take them back into that coop at night so I can lock them up away from predators.
One thing that I think helps is that I have a lot of room. Mama needs a certain amount of room to work to keep the chicks safe, but the big need for room is after she weans them. I’ve had hens wean their chicks as early as three weeks after hatch though most go a lot longer. The chicks are left on their own with the flock to handle pecking order issues themselves. They are already integrated, Mama took care of that, but she doesn’t do anything about pecking order issues. The chicks have to handle that on their own as they mature.
Many people like to separate the broody hen and her chicks from the flock while she raises them. Then they have to integrate the broody hen back into the flock when she weans them and integrate the chicks at some point. They have their reasons and for some it’s the right choice.
Of course there are all kinds of variations of any of these. We all do things in our unique ways. Hopefully you will get some broody hens and try yourself. Good luck!