How would you like to be forced into a same sex relationship?
Disregard that if your in one and think about how you would like to be forced into a relationship with someone your not interested in.
Two males budgies can live together but it's not natural.
Why don't you want them to breed?
If your really concerned about babies, let them lay a clutch of eggs and then replace the eggs with dummy eggs (available from pet shops). Dummy eggs are just plastic eggs you put in the nest when you remove the real eggs.
But there is nothing wrong with them breeding and it simply means they are happy. And you can always sell the young. They only have 3-5 babies so its not like fish when you can get 500 young.