Lots of things to unpack here... hope we can help!
Are the parent birds being health tested at all? Are they related, like brother and sister, or father and daughter? It's important that birds being bred are healthy and are not related to keep from having weak offspring.
What is their diet, what do you feed them while they breed?
When are you pulling them from the nest? What are you feeding the babies to eat, and what is the temperature and consistency of the formula you're feeding?