As the others said, I wouldn't worry too much about the ones you lost. Sometimes they just aren't meant to be.
I try to be firm with myself that I'm going to let them pip on their own or not at all... and I rarely have the patience ... with my eggs last year I only was firm enough with one small clutch of 5 eggs, 2 slit, 3 rocked like crazy...then stopped... all five were deformed.
It's cool that you have some nice babies to work with though!
Sounds very neat. My kings are only just in the first 3rd of their gestation, I have quite some time before they lay, then the long wait until they hatch!