Good questions but you don't get guarantees with behaviors of any living animal. Broody hens hopped up on the hormones that make them broody can be even more unpredictable. In your situation there are many different things that can possibly happen. No one can tell you what actually will happen for you.
Some of us let broody hens incubate, hatch, and raise the chicks with the flock, we don't isolate at all. Others isolate at different times. I never bother a broody hen during the actual hatch but others can't keep their hand out of there. There is no set way to do any of this. They all have their benefits and risks.
Many people let multiple broody hens incubate eggs in the same room on their own individual nests and have no problems whatsoever. I remember one photo where there were five different broodies, each in their own nests, in a bank of nests and the poster said they did that all the time with no issues. Those were with the flock, not isolated in a garage or somewhere else. So it is possible you can leave them where they are, do nothing, and things will be great. Each hen and her chicks will imprint on each other and they will raise their own.
Sometimes broody hens will fight over chicks or eggs. I had that happen once. A hen had just gone broody when another hen had eggs start to internal pip. When the chicks internal pip they start chirping, talking to the hen to let her know they are on the way. The new broody decided she wanted to take over that nest, they destroyed about half the eggs in that nest fighting. The same kind of thing can happen after the chicks hatch, one might decide she wants to adopt and fight the other hen for them. It's possible chicks can be hurt during this fight but if they are off the nest, probably not.
Sometimes in that situation instead of fighting the hens decide to work together to hatch and raise the chicks. That can happen early in incubation or anytime after. There are several cute photos on this forum of hens working together to hatch the eggs or take care of chicks.
I've never seen it but some people say one broody might try to kill another broody hen's chicks. This might be when they are sharing a nest and chicks hatch under the other broody, when they are in separate nests and a hen is hatching, or when they are out roaming with their own chicks. I don't know how common this actually is but it is possible.
No one can tell you what will actually happen with your chickens. We can tell you our experiences and what might possibly happen but with living animals you just don't know. As far as I am concerned there is no right way to do this where every other way is wrong. Good luck!
