Can a hen who's sitting on eggs be left in the coop with all the others or will the other chickens peck her and attack her chicks when they hatch?
Chickens have been hatching eggs and raising chicks with the flock for thousands of years. That has been the normal order of things on small farms since well before Roman times. The Egyptians kept chickens this way, probably plenty of other ancient peoples did too. Chickens are living animals with their own personality so disasters can happen, but in that set-up they typically don’t.
The normal model for that though was that the chickens free ranged. They were not shoehorned into a very tight space. And it is possible to get an aggressive chicken, usually a hen when it happens. Most mature roosters are more likely to help a broody with her chicks than harm them. And occasionally you get a broody hen that won’t protect her chicks. Again, this does not happen often but it can and does occasionally happen. They are living animals. I can’t give you any guarantee of what will happen with yours, but I can tell you that mine hatch and raise with the flock.
How do I know what eggs to take and what eggs to leave for her to hatch?hatch?
There is no practical way for us to be able to tell if an egg is fertile or not without either cracking it open or incubating it to see if it develops. Scientists can do it but I don’t have an advanced chemical lab in my coop.
You can crack some eggs and look for the bull’s eye. I’ll give a link to directions. If most of the eggs you crack are fertile, most of the ones you don’t crack will be fertile too. You have to take some things on faith.
Fertile Egg Photos
https://www.backyardchickens.com/forum/viewtopic.php?id=16008&p=6
The best thing to do if most of them are fertile is collect them for a few days to get all you want her to hatch, mark them so you can clearly tell which ones need to be under her, and start them all at the same time. For eggs going under a broody I take a Sharpie and draw two lines around them, one the long way and one the short, so I can tell at a glance which ones belong. I check under her at the end of the day and remove any that don’t belong. These are still good to use if you collect them every day.
Some people isolate a broody when she is on the eggs or after the eggs hatch. Some of these do it because someone on the internet told them that have to. But some do it because they have experienced problems trying to hatch or raise with the flock. We all have our unique set-ups and management techniques. It’s not that one is right and one is wrong, it’s just that we do things differently. If someone says that you absolutely have to do something a specific way with chickens, I get a little leery. I see things on here all the time where people tell me you have something do it a specific way. Well, a lot of those times I don’t and I still do OK. You don’t have to isolate a broody on eggs. You don’t have to let her hatch with the flock. Either way works.
Back to the OP. I get the feeling you are not asking for advice but are looking for confirmation your method will work. The way I understand what you are wanting to do is to separate your flock. Keep some hens separate from the rooster and collect those eggs to use. Isolate some hens with the rooster and leave the eggs to build up, thinking this will cause a hen to go broody so she can hatch the eggs.
You can certainly try it this way. I think you may be disappointed but it may work out for you. A hen does not need a rooster to go broody. If one of yours goes broody, don’t be shocked if it is one of the ones not with the rooster and not with eggs building up in the nest.
There are people on here that think it helps a hen go broody if you let the eggs build up, but it is not a guarantee. Many people have tried that and been disappointed. I’ve added a golf ball a day to a nest until I had a dozen then left those for a month during late spring, a perfect time for a hen to go broody. Nope, did not work. Certain hormones have to kick in for a hen to go broody. I really don’t know what triggers those hormones. Part of it is hereditary, a pretty big part but still only a part. Many hens will never go broody in their life. Some go broody regularly. Some breeds, usually the ornamental breeds not the utility breeds, go broody a lot more than others. But there is still no guarantee with any individual hen.
As I said you can try it. You may get lucky. I really hope so. But if you want to be assured of getting chicks you might wind up doing what I did. Get an incubator and a brooder. That’s the only way you can exercise absolute control over the situation. Any time one of my hens goes broody she gets hatching eggs but to get enough for my freezer, I use the incubator.