The first time is a steep learning curve for you, isn't it. If you want to discuss some of the things you could have done differently for next time let me know, but I'll try to concentrate on point forward. You have blocked the broody off so no other chicken can get n there to lay an egg. Good first step. You candled the eggs and gave the best developed to the broody hen. Another good move.
Lets use your assumption that the youngest in the incubator are 10 days old and the oldest are 14. It could be worse. An egg needs to be turned early in incubation to keep the yolk of developing chick from touching the inside of the porous shell and getting stuck, which would be fatal. Turning also helps body parts form in the right places. By 14 days a membrane has formed around the developing chick to protect it from touching the inside of the shell and body parts have formed. You do not need to turn them after 14 days. You put them in on the 1st and 14 days after that, the 15th, I'd stop turning them. The oldest eggs by your estimate will be 19 days old.
The other part of lockdown is humidity. An egg needs to lose enough moisture through the porous shell so the chick has room to hatch and an air supply to breathe after internal pip. There are other benefits too. The good thing about this is that Mother Nature gave us a reasonable window of moisture loss to work with. The other part is that if it becomes too dry that membrane that protects the chick from touching the inside of the shell can dry out and shrink, wrapping the chick so tightly it cannot move to hatch. This is why we typically raise humidity levels during lockdown, to try to avoid shrink-wrapping the chick. This is the hard part of knowing what you should to do.
The reason we typically up the humidity at day 18 is that chicks do not always hatch at exactly 21 days, whether under a broody hen or in an incubator. I've had broody hens hatch a full two days early. The biggest danger from shrink-wrap is after the chick has external pipped, so we try to up the humidity before the first egg pips. Upping the humidity after 18 days gives you a safety margin. The situation you have to deal with is that you don't have much safety margin to work with. You are trying to salvage what you can.
I don't know what humidity you have been keeping that incubator on. You can find photos of candled eggs to see where you should be with the age of the eggs but you're a bit nebulous as to exact age. To me trying to estimate where the air cell is in those eggs is a pretty rough guess at the best even if you did know the exact age. Still, using your assumption that the oldest is 14 days I'd look at that one and see if I thought I needed to drop the humidity a bit to catch up. I'd worry about the oldest ones only and let the younger ones do what they are going to do. To me that is the best you can do.
Keep an eye on those incubator eggs as you get closer. Tap the incubator to see if you hear a chick peep back. See if you you see an egg wiggle. Those are signs that a chick is getting ready to hatch. If you see that go into full lockdown mode immediately. Stop turning and up the humidity. Now!
Another thing. When the chicks hatch they crawl around, pooping and spreading slime. They can make a mess of the later eggs. I don't know what your incubator looks like or how big it is, but I'd try to isolate the early hatchers as determined by candling. Maybe make open topped boxes out of hardware cloth that you can invert over those eggs, either each one by itself or at least in bunches.
It's quite possible your incubator will start stinking pretty badly a few days after hatch from the slime and poop. You've probably heard to not open the incubator during lockdown. Ignore that, you are not in a normal lockdown. If you need to take a chick out, take it out. If you need to take the incubator apart to clean it, clean it. One trick to keep the humidity up while you are doing this is to steam up a bathroom and keep the unhatched eggs in there in the high humidity.
If that hen hatches some of her eggs but not all, you can try putting some of them in the incubator to finish hatching, especially if candling shows they are still alive. That means starting lockdown immediately. You have to stay flexible with this.
I wish you luck.
Lots of thought and time went into the above reply. A perfect response to your questions.
