An ounce of prevention is worth a pound of cure. The next time you want a broody hen to hatch, collect all the eggs you want her to hatch, mark them, and start them all at the same time. Then, every day without fail after the others have laid for the day check under the broody hen and remove any that don't belong. While anything can happen with living animals that should eliminate the biggest risk of a staggered hatch.
It may not just be the hen collecting eggs. That does happen but often other hens will lay eggs in the nest.
Another option is to isolate the broody where other hens cannot get to her nest to lay eggs and she cannot get out to steal eggs. A lot of people isolate their broodies like that. There are usually different ways to handle situations. Still, start all the eggs at the same time.
There are some misconceptions about turning. Early in incubation turning is important. Turning helps body parts form in the right locations. Turning helps keep the yolk or developing chick form touching the inside of the shell where it can become stuck. If it becomes stuck it is a death sentence. But by two weeks all body parts have been formed and a membrane has developed around the chick to protect it from contact with the inside of the egg. That's a good thing because the developing chick will soon be so big it will be forced to touch the inside of the shell.
Bottom line, after about two weeks turning is not necessary.
The other side of this is that it is not gong to hurt the hatching chick if the egg is turned late in hatch. You may have noticed the first chicks that hatch often play rugby with the unhatched eggs while waiting for them to hatch. I don't like to see the pip get moved so it is faced down flat on the bottom of the incubator, as long as the chick can breathe at the pip it is not a death sentence for the egg to be turned. They will still hatch.
Your concerns on turning are overrated, at least in my opinion, though they are common on this forum. The real issue to me is the humidity. You want the late eggs to lose enough moisture so the chick can pip and hatch, but you don't want the early hatchers to dry out and get shrink wrapped. I don't have any great suggestions to handle that in a staggered hatch, especially if you don't have a good handle on how long they have been incubated. Whatever you do might be good for some of the eggs but bad for others. All I can suggest for that is to candle and try to guess about how far along they are and do your best.
Another issue with staggered hatches is that the chicks make a mess when they hatch. They start pooping pretty quickly and they often slime things until they dry off. That can promote the growth of bacteria in the incubator which can cause it to stink and may get bacteria into the unhatched eggs, killing the chicks. You may want to clean the incubator really well after a few hatch. I just don't like staggered hatches but it sounds like you are going to have to deal with one. Just do the best you can and good luck!
