I hate to say it, but not grinding the food may have contributed to your loss. Birds have such a high metabolism that if they aren't eating almost constantly (especially as chicks when they're doubling in size every few days), it can really affect their health.
I wouldn't use sugar water. I might add some Nutri-Drench to their water after the stressful trip, but only for a few days. I've heard people swear by fermented food, but I've never tried it. I don't know if it would be okay for chicks, but it's fine for adults.
That's awful to hear about all of the dead chicks. I've never shipped live animals (except for black soldier fly larvae and I'll be ordering live fish soon), but it always worries me that they won't make it.