No problem. We are all here to help one another.
Marking a few air cells lets you know that the eggs are on track for hatching. That air cell should expand and grow larger as the chick develops. Do a search for air cell development here on BYC and you should come up with a chart that shows air cell development on a healthy egg.
Your hens may surprise you. Mine are super friendly but generally turn into little velociraptors when I reach under them to candle eggs. Try to reach under from behind if you can. My hens generally just glare at me and give me a good peck until they see that I'm giving them their egg back. When I do that, I just put the egg at her breast feathers and she will tuck it under herself. Kinda distracts her long enough for me to snatch another egg out from under her.
Thank you very much for this advice on approach. I dod this and although she made very angry noises at me though the process, she didnt run or bite, and not even a peck!