Pick them up one by one and hold them to your ear, and give them a little tap with your fingernail. Sometimes you can hear tiny tapping noises coming back at you if the chick is getting ready to pip. You might even hear cheeping from inside the egg. And even if you don't hear any of that, give the egg a good sniff. As long as it doesn't have any faint rotten whiff about it, you're probably good to leave it under her for another day or so.
Edit: That's what I've just done with mine. I've got one chick out too, a couple halfway there, and one egg unpipped.
When I listened to it, I could hear it cheeping in there!