Hi, welcome to BYC!
Sorry you are having issues.
Where are you finding these dead chicks? All hatched chicks should be UNDER a hen. If they hatch in the middle of the night, they should not be out from under the broody yet. They are usually still getting their land legs. IF they are getting out from under the broody, they may not know how to find their way back and chilling to death. For this reason I usually check every half hour or so, and have found many a chick lost their way after getting out from under mama to eat or something. But those aren't fresh hatches. Fresh hatched chicks are not that mobile for the first 24-48 hours, in MY experience.
One possibility in that the eggs are actually too dirty and dying from bacterial infection after hatching. My broody hatched eggs sometimes end up covered in poo. And that is one reason for chicks to die very close after hatching. Someone recently had all their chicks die shortly after hatching, and it was in an incubator. So I would definitely consider it a possibility.
No, I don't think being pecked will necessarily leave visible injuries. It's also possible it is being caused by other flock members. If they say play a game of keep away like they do with other curios finds, all the commotion could be very stressful
IF it were me, and I had an incubator.. I would take all the eggs and finish hatching them and try returning to the broody after they are hatched all together, leaving duds under the broody. Though my broody's will continue to sit on air.
Also, hens can accidentally stand on the chicks while adjusting themselves or the nest. I have seen it happen with the chick squealing up a storm to the oblivion of the hen. Chick would have surely been dead were I not there to intervene.
Agreed temp to low is more likely than temps too high from what you describe.
If you leave them under the hen, I would be out at dawn checking before any flock dynamics started. And with fresh chicks I usually supervise during morning dispersal to make sure nobody is bullying.
Hope the rest of your hatch goes well.
