Going forward, don't add more eggs when you already have a batch going, unless you plan to buy a second incubator to move the eggs into as they lock down. Now you're going to have to deal with trying to lock down some eggs while having other eggs that are not ready yet.
This means you're going to have to take the turner out so you can lay the ones that are locking down onto their sides and stop turning them, but then the other eggs are still going to need to be turned, so you'll have to do it by hand.
And you'll also want to increase the humidity for the ones in lockdown, but the ones not in lockdown would actually need lower humidity to continue to lose moisture at the proper rate. You can't do both of those, since that would be impossible.
In addition, you'll have to keep opening the incubator at least three times a day to turn the ones that aren't in lockdown, and of course that's going to let the humidity out, which is not good for the ones that are going to be hatching.
So, going forward, don't add more eggs until the last batch is hatched, unless you have or are planning to have a second incubator.
As to your questions about some being more developed than others, is your incubator still air? Still air styrofoam incubators are notorious for having hot and cold spots. Some of the eggs could be in a cold spot, and if you haven't been rotating the eggs around the incubator to equalize this, it means some could be less developed because they haven't been at the same temperature as the others.
I'm not sure what you mean by the heart moving into the air cell, can you post a picture of you candling one of the eggs with this problem?
