I breed and a good way to get them into breeding condition is extend the day by putting a light on in their roost. Budgies will naturaly go into breeding condition in the wild when the days grow longer.
Spray budgies with luke warm water every day it perks them up. Give plenty of food and let nature do the rest.
One point when they have hatched the eggs put a night light in the area of their cage as this will help mum to find her way back to the box if she has to come out of a night time. If she can't get back the chicks will die.
Good luck and keep us posted.