Chirping from inside egg in incubator

[Storm3]

Hey all..It's day 20 for me..I have a big clutch incubating..40 eggs, and one double yolker..Last checked day 18, all babies still alive, as well as the double yolker..Just a question here, when I hear the first chick peep, should I find the second chick peep and make a small hole..I'll take before and after pictures. Lost power three times during this incubation do to storms, they all survived that ordeal. The daddy roo is either a Blue Austarlorp, meanest rooster there ever were..or the part silkie/part comet rooster..I don't even know from which hen this egg came..I think one of my comets. The egg is huge, I'll post pictures of that in an update..Any help as to what to do would be great...At last view on candling, the air sac was quite large, and th rest of the egg mostly full, so I could still see the little chick move on the bottom, and the other also.. See if I can get my son to video this segment, if not he'll do stills of the hatching..I need to know when to intervene...Any help would be great..thanks peeps..

Diane