Help with pipping but no chirping (ducks)

[Baylor]

I just got back into town and should have come home to 3 new baby ducks. I didnt see them shaking in the small incubator so I candled them to see that they have all internally pipped but there is no shaking that I can see nor hear any chirping. Should I intervene?
I know they were a good pair for parents because 3 just hatched last week successfully. The parents were taken by something in the wild so these little guys are their legacy.
I have read oodles but just am not sure exactly what I should do. I did just externally pip slightly at the tips the shells and still I dont hear anything.

 

[cmom]

If you try to intervene most likely the chicks will die. Sometimes you may hear peeping and sometimes not.

ETA: What day are you on and how has your temp and humidity been?

 

[Baylor]

I couldnt sleep so I intervened at 2:00 am and all 3 were dead - very sad since their eyes were open and it appeared there was no blood veins around the membrane so not sure what stopped them from externally pipping.

I think if I would have intervened as soon as I got home I might have been able to save them.