After you drilled a hole did you cover it or just set it back in the incubator open?
Egg B, the one that hasn't pipped yet sounded Monday morning, while Egg A which did pip on it's own sounded Monday night then they both sat until Wednesday when Egg A pipped after I whistled to it. In Egg A the membrane has really drawn down onto the chick as you can see in the picture and even before that Egg A was much noisier with the 'wet paper bag' sound.
Should I just use an eyedropper and add a drop of water in through the hole to have a look? I'm happy to just wait and see what it does for now, I certainly wasn't expecting them to pip and hatch at the exact same time, I just poked the small hole this morning as a precaution because it had been 4 days since the egg sounded with no external pip, the other one pipped on it's own last night.