I don't like staggered hatches in one incubator, too much stress. Most people that do staggered hatches on any kind of regular basic use two incubators, one as an incubator and the other as a hatcher. So that is one pretty stress-free solution for you, get a second incubator now and start tweaking it to get conditions right.
Let's look at some of your issues. Turning helps keep the yolk or developing chick from settling and touching the insides of the porous shell where it can get stuck. That would be a death sentence. Turning also helps body parts form in the right spot. By two weeks the body parts have formed and a membrane has developed around the chick to protect it from getting stuck to the inside of the shell. At some point that chick gets so big it has to touch the inside of the shell. So after 14 days you don't really need to turn them. You could probably get by with a bit less than 14 days, I'd guess that is a very safe number.
The purpose of humidity is for the porous egg to lose a certain amount of moisture. There are different reasons for that, not just the size of the air cell. Nature was nice enough to not make that a hard precise number, rather she provided a range where that works. Each egg has its own "best" humidity. It can vary because of the porosity of the egg, how thick or thin the egg white is inside the egg, and how and how long the egg was stored before incubation started. The egg will lose some moisture as it is stored so they don't start off even. If nature had not provided that window of moisture loss that works chickens would probably be extinct. I don't know what humidity you normally use when you hatch, what works best can vary depending on the incubator, the temperature and moisture level of the air going into the incubator, and even your height above sea level. During incubation it is not about an instantaneous humidity but more of an average over the entire incubation period.
The reason we increase the humidity during lockdown is that the membrane that forms to protect the chick from touching the inside of the porous shell can dry out and shrink around the chick, preventing it from being able to move to hatch if the humidity level is too low. The most dangerous time for that is when the chick has external pipped. That does not happen all that often, even if you open the incubator and let the moisture out after pip, but it can.
When a chick first hatches it is wet. It can slime the incubator and the other eggs. Also, the chicks soon start pooping. That poop can mess up the other eggs but it also will start stinking in two or three days. That can create a problem for staggered hatches.
I don't know what your incubator or turner look like or how long those first eggs have been in there. Can you remove parts of the turner so you can create a bare spot for the first group of eggs? Then build an open-top box out of hardware cloth and put that up-side-down over the first eggs at lockdown to contain those chicks when they hatch. That would solve the turning and first chicks messing up the later eggs issues. If you cannot take part of your turner out I'd take the turner out at lockdown and put that box over the first eggs or find some way to keep the first chicks away from the later eggs.
Since it seems the second set may be a bit more precious than the first I'd wait a bit to go into lockdown since the eggs are 7 days apart. The timing on this gets really tricky because it is not all that unusual for chicks to pip early, as much as two days. That's why normal lockdown is three days before hatch, to catch the potential early ones. I'd probably wait a day to go into lockdown, but if you see any movement or hear any peeps I'd go into lockdown mode immediately. That could happen while you are sleeping, you may wake up to pips of even chicks so don't cut it too close. Plan on doing it at your bedtime unless you see activity. If you do run into an early pip one trick is to steam up your bathroom and store the eggs in there while yo are setting up the incubator.
On the humidity. I'd probably just run humidity as normal for the first eggs and take my chances with the second set. You will probably be within that window for both sets. If you wish and have a way to control it you can try running the humidity a tiny bit lower for the first set or even go a day at pretty low humidity early on. It's average that counts. This is probably over-micromanaging it but you can tweak a bit if you wish.
After you remove the first batch of chicks I'd clean and sterilize the entire incubator to get rid of slime and poop. The reason it will start to smell is that bacteria is growing in it, that can kill the second set before they hatch. I had one hatch stretch out over two full days. It was starting to stink before I managed to get it out and clean it.
I know this is really long but I wanted you to see why I'm suggesting certain things. Maybe you can come up with your own solutions. Do you know anyone with an incubator you could borrow for a week or so?
Good luck with it.
