There is something called BluKote available at the feedstores that you can use to stop the other chicks from pecking at the scratched one.
I am sorry about the Dead in Shell one, those are always the saddest.
I would take each egg out quickly and listen very carefully for any peeps, candle it with a bright flashlight and see if you see any movement. Any peeps or movement go back in the incubator.
You can also do the "float test". Take very warm water (tap water that feels warm but not hot i.e. approx 100 deg) and fill a bowl. Check the egg to make sure there are no pips/holes in the shell. Put the egg in the warm water. If it wiggles in the water its still alive (wait about a minute). Take it out and wipe it off and put it back in the incubator if it wiggles. If it floats, it may still be alive,check it. If it sinks.. toss it.
On the questionable ones - you can make a teeny hole at the top of the shell. Peek inside to see if you see anything. Make the hold larger very slowly.. if you see bleeding stop immediately and put it back in the incubator. Slowly take away the outer shell until you can see what you have inside.
3 days after hatch is probably the latest I would leave them in - although somebody said they had one hatch on day 27. If you check them all and determine if they are alive or not you can put the ones that just need more time back in.
Good luck, I hope you find more wigglers!