if you've made a hole in the air cell end and can hear chirping I think you are ok. If you can do it carefully you could start picking a bit at the hole that you've made to make it bigger. If you see any veins or blood STOP! Here is a good guide to assisted hatching so read it carefully before you delve into this. You said the shells are very hard so you just may have to help.Hello sorry to jump back in , but one of the eggs I candles yesterday was fully internally pipped some yellow bruising on the shell this morning so I took her/him out and candled again, still moving but no chirping and nowhere here the movement I gently drilled a hole in top. Straight away I could hear chirping. The hole is only teeny as the egg was near on impossible to penetrate! It wasn’t soft like the videos I watched. Does this mean humidity is too low? Can I resolve it now!? All eggs moving but no sign of any pips yet and only small movements around membrane line !? Should I be assisting them all!?
https://www.backyardchickens.com/articles/guide-to-assisted-hatching-for-all-poultry.72886/
If your humidity is about 80% you should be good. Do you have a humidity gauge inside the incubator or are you depending on what the incubator says it is? I would not trust what the machine says. I always put one right inside the incubator. If they are all moving I would be pleased. I'm sure you are not in the USA since you are using Celcius for temperature but if you have a Walmart you can pick one up there that has both the temperature and humidity. They are a little over $10 and you can set it to celcius.