Second egg is definitely dead--I floated it in warm water for a minute and there was no movement at all. I'll open it tomorrow to see what happened, then bury it in my garden.
Hairline cracks had gotten a bit bigger in the older egg and pressed a tad outward, but still no pip. The movement in the egg had been decreasing pretty significantly the last two days; I was checking in every two hours or so and saw barely any movement all day.
I hope I made the right decision--I went into the egg, chipping away a bit where the cracks were. I don't think the baby was in the right position, and the membrane didn't look quite as bad as the glued-to-chick pictures Susanne has, but it was a bit dry and had separated from the egg pretty significantly. I wet the membrane with 100F distilled water (I hope that was a good temp!). I could see only one tiny vein left in the membrane and it was clear, so I enlarged the hole I'd made in the shell and took a toothpick and enlarged the hole near the beak so the whole head was free (the hole he'd made was tiny and just had his eggtooth through it). I got a big chorus of chirping once his head was free, and then he went quiet for a bit. I let him sit under the heatlamp for a bit to see what he did.
He's been sitting for about three hours and has now started chirping a lot. I hope that means he was ready and I didn't jump the gun.
(I have THREE thermometers in there and they each show a different temp

The temp is 97.8 in the one I trust the most, but the other two show higher so I'm going to leave it there just in case)
He's got long yellow down but I can't see a yolk sac at all, so no idea if it's absorbed or not. I'm going to leave him overnight, checking every hour, to see what he does. He's gotten really talkative in the past hour so hopefully he's having contractions and pulling in his yolk sac.
He's got something in his mouth--I can't see clearly, but it looks like he's got a little black string on his tongue. Could that be part of the membrane he bit?