Well, I can answer the general part of that question, Crystal. Then Sphinx can tell you the rest: were the eggs the same age and how long she will leave them in. (Although she did say in her last post that she would probably take them out this morning carefully and wait for others to hatch).
Chicks can leave off of the absorbed yolk sac for up to 3 days. That's why hatcheries are able to ship newly hatched chicks. So you can leave the already hatched chicks in the 'bator til the rest hatch. Theoretically you shouldn't open the 'bator after lockdown b/c it can really mess with humidity levels and cause remainder of the eggs to not hatch. Many people do, however, and will give you tips on how to do so as safely as possible without disrupting the hatch.
As to why some chicks hatch earlier than others if the eggs are the same age: they are just like human babies - some just grow/develop faster than others. Babies are born when they are ready! That's why chicks can live for 3 days on nutrition from the yolk, so the hen has time to hatch them all. She instinctively will abandoned the remaining unhatched eggs once she knows it's time to take the existing chicks out to forage for food - she just knows when it's time. You'll notice that when a broody begins to hatch eggs, you'll see that first one and you have to patiently wait up to 3 days for the rest to hatch. It can be nerve-wracking!
And if you are new to chickens - as I was 3 years ago - the best thing you can do is incessantly prowl these forums. Everything I've learned has come from here. Invaluable. I started with 5 hens and a rooster a little over 3 years ago. I now have 28 hens, 2 roosters, growing babies of different ages, more on the way via mail in March, and I'm starting on turkeys! As a matter of fact, I've been able to nurse a couple of chicks back to life thanks to what I learned here.
Thank you, BYC!