Welcome to the forums!
It takes 18 days of incubation on average for budgie eggs to hatch. Depending on whether the female has started to fully incubate from the time she first laid the egg, it can take up to 21 days till you see a chick. So generally the time for them to hatch is anywhere between 18 to 21 days.
I agree with Cathy, if you want to give your budgie couple the best chances for them to raise a family in a stress free environment, you must put the breeding pair of your choice into their own cage and without the presence of any intruder bird.
You must also make sure your pair is properly conditioned and is on a good breeding diet with a calcium source before allowing them to go through the task of breeding and raising a family.
The fact that your budgie ate her own eggs is not good. I have experienced this in the past and in my case, my budgie would always eat her eggs even despite having an excellent diet and good calcium source. After 3 failed attempts I decided to take her out of my breeding program.
Regarding your current eggs, they are either infertile or you have dead in shell chicks. By this time any egg with a dead in shell chick should have a greyish looking appearance. In some cases you can see a reddish ring of blood going across the eggshell.
There is a lot of info about this subject on the stickies at the Breeding section of the forums and I suggest you go through them if you haven't done so already.