Are your temps fluctuating a lot? I know a high spike will kill off an egg, even late term. Other than that, too much humidity and you can have neonates drown in their eggs.
Laura, I don't think eggs being pushed by siblings late term really does anything. I've seen babies turn, and roll around in their eggs late term while candling. They aren't so much "attached" to the wall of the egg as they are when they are in the embryonic/cell splitting stage. I also talked to a member who experimented and turned her eggs throughout the incubation period and she never lost one.
I candle my eggs when they're laid to get an idea of how "strong" the embryo is. I would suggest doing this. Really faint or nonexistent red and you can kinda of prepare yourself in case the embryo isn't going to be strong enough to survive.