Hello! There could be several issues.
1. You could have two females. Are they DNA sexed?
2. They may be too young to reproduce, generally they are supposed to be at least two years old before they should be breeding. Before that and there can be infertility issues.
3. If you are sure they are male and female, perhaps the male is not getting the job done, he may be inexperienced and not mating correctly to fertilize the female.
4. If they don't sit and incubate the eggs, they get cold and die. Often times eggs are abandoned and left to die.
Hope that helps a little! It's hard to get it right....and should not be taken on by the inexperienced.