Hatching parakeet eggs

This is about the problem of a parakeet owner about the failure of hatching the eggs. During his school years, my husband was taking care of parakeets for an informal business. He bought a pair and his plan was to breed and sell. He made a computation that if the birds would hatch 2 eggs, he could easily recoup the expenses particularly the cost of the bird seed. It was encouraging to watch the birds do their thing and it didn't take long before the female laid an egg in the square box serving as the nest.

But days and weeks passed, there was no baby bird. The 3 eggs in the box remained eggs that were already spoiled. The box was cleaned and again, it did not take long for the female to lay the second batch of eggs. But the hatching did not materialize. My husband consulted their neighbor who is a vet. The advice was to get 2 coconut shell (with a husk), tie them together with a wire so they would look like a whole coconut with the brown husk. But make a hole so the bird can enter. On the third batch of laying, it didn't take long for the surprise to appear - the head of a little birdie. It was only one baby bird but  that was the start of a good business.

From my personal experience, it is actually not so easy to get parakeets to reproduce properly. My own budgies tried multiple batches of eggs without success. Not only it is said that young birds need to gain experience through trying before they can succeed, but any kind of sudden noises or changes in the environment can make them abandon their eggs or even the little chicks. On multiple occasions, my budgies pushed their own eggs and chicks out of the nest. I had to remove the bird nest from the cage after 4 failed tries if I remember correctly. Too bad, I would be very happy if even just one chick could grow up nicely.

So how many little birdies had the parakeets successfully raised in your story after the first one?