My zebra finches hatched today but one of them is dead why is this?

one of my pairs of zebra finches eggs all hatched today two this morning and the last one any time between 8:00 pm and 11:00 pm as this was when i last checked them but the last one that hatched was dead when i looked it had no toes i think that its not developed properly and the parents cracked the egg or something. also how can i tell if they are being fed i have baby budgies they are Nearly a week old now they are doing fine but i don't know how to tell if the finches are being fed or not as they are so tiny can any body help my questions?