I had the same fun. A lady brought over some eggs that her peahens got off of - as 5 hatched. We had no idea if they were even viable anymore or how long till they would hatch, and they were so dark, I was unable to see anything. A week later, with me turning them and keeping the incubator about 40%, I went to candle - see if I could see internal pipping, and got chirped at. 3 hatched. My trouble is that I keep losing some of them. I don't ever see anything wrong, just find a dead peachick.
Can you candle them? The only thing I could tell on the 3 that hatched, was that they were totally dark within .. so they were fairly fully developed. The other few I could see into and they never developed to where I could see veining - I left them for a few more days, but they never started growing. It would give you some clue.