I can help some. Wether or not you leave them with the broody hen depends really on how she is and what you want from the chicks.
Is she a friendly hen? Or does she run away from you? If she's a friendly hen and will bring the chicks to see you, I'd let her raise them. Nothin is cuter than watching chicks with their mama, IMO. I WOULD make them a little pen for safety for now though. If the hen is NOT friendly and runs from you, the chicks will learn this behavior also, and you will have scared chicks that dont want to be handled. In this case, I would catch them and brood them without the help of the hen. She would be fine to go back in the coop with the others, and hens will "forget" their chicks after a few days. If you raise them yourself, and handle them often, you will be more likely to end up with friendly chicks.
When the other ones hatch, you can put them together and raise them all if YOU are raising them, but I wouldn't put other babies in with the hen and her chicks, as she may see them as "invaders" and hurt (or kill) them. Also, size difference is something to take into consideration, as these chicks are already born, and the 'egg' chicks are only on Day 5 or so. So....I'd guess that the current 'live' chicks will be somewhere around 2- 2.5 weeks old (you have roughly 17 days until the eggs hatch if they're on day 5) by the time the new ones hatch. Thats good in that a 2 week old chick is still pretty calm, and shouldnt pick TOO much on the smaller, younger ones. But again, this is only if YOU are brooding them yourself, not with the hen involved. I just wouldn't try it. There ARE tricks to getting it to work, like slipping the new chicks into the brooder pen at night one or two at a time so she (the hen) doesnt really notice them (since hens cant count) but I've not tried it myself, so I cant say it will work. I HAVE mixed together day old chicks with older 2-3 week old chicks when I was brooding them and had great results.
I wouldn't just let her into the coop with the babies, as you have no idea how the rest of the flock will treat the "rodent snack sized" new comers, who at this size and age are deffensless. I would corner off a section of the coop and make a little pen with chicken wire so the flock can see them and get to "know" them before allowing them access to each other. And you will need to get food and water to them all.
When I moved my newest chicks out to the coop, I first put them in the attached pen so they could meet. I kept them in that pen until they were 3 and 4 weeks old (I had a week difference in ages) and then I cut a hole in the pen small enough that the little chicks could fit through, but too small for the bigger chickens. This worked great because if the bigger chickens got to rough for the chicks they could run back into the pen for safety. After another week or two of that I finally closed off the hole and they have been living in the coop with the big chickens since then and I've had no problems. They now get to free range with the big birds, and my bigger chickens even watch out for them.
As far as the hen putting up a fuss, yes she might if you grab all the chicks at once and run with them. But remember that chickens cant count, so if you followed her around and grabbed one here and there, allowing time between, she may not even notice. Leave her with one or two for a day and then take those too, and you'll have much less fussing. Plus, she'll be eager to get back into her "flock" in the coop.
