Have you every tried to return them to the flock?
I disagree with you completely. When a hen is broody, she is at the top of the flock pecking order. Even the roosters won't mess with her. When she has chicks, there are hormones in her body that cause her to defend those chicks at all costs. As the chicks get older, those hormones lessen and she becomes a lot less protective. At about 5-7 weeks old, she'll abandon them completely.
If you put the broody and her chicks in the flock at 7-10 days old (some people have her hatch her clutch in the same coop as the rest of the flock so they're with the flock from day one) her hormones will be very high. She will protect the chicks and stop other hens from taking an interest. I've even seen my broody hen take food away from my alpha hen to give to her chicks. The roosters (and we have four) have no interest in the chicks whatsoever. If you wait until the chicks are feathered, they are going to have a much harder time without Mama to look out for them.
We have 75 hens and four or more rooster at any given time. We hatch almost all of our replacement birds under broody hens. We put Mama and her chicks into the chicken pasture as soon as we think they chicks can navigate the steps to the hen house, around 7 days old. We've never had a chick killed by a flock member except when we had a broody that was simply a bad Mama--she sat OK, but didn't care for her chicks and they had to be taken away from her and she was never allowed to hatch eggs again.
Remember, a hen is SUPPOSED to return to the flock after she sits. She wants the protection of the flock and the rooster for herself and her babies. Chickens are flock animals, and have been raising chicks a long time before humans decided that we know how to do it better. If a hen couldn't take her chicks back to the flock until they were fully feathered, chickens would have died out long ago. Mama hen is prey for every predator out there if she's by herself and can't fly away because of her chicks.