but you shouldn't encourage breeding if they aren't producing chicks.
To add to what Brian has written above;
...and also if you don't actually want chicks.
Birds in captivity are not like in the wild. In the wild they would do their own thing and breed when the conditions are right.
In our homes, the conditions are more often than not right, so they can over breed, laying too many eggs. Cockatiels are notorious for becoming chronic egg layers, which can be dangerous for the hen.
It may seem like we are doing them a favour letting them endulge in "natural instinct", but they are not wild, and there's nothing natural about birds in our houses.
Having dummy eggs is a great thing to have when living with females. Even if you decided you wanted to allow your birds to breed and have a couple of chicks and keep them, you can still use the dummy eggs to make the clutch smaller so you have two chicks instead of six.
You can use the dummy eggs to lessen eggs laid in general, alongside other tricks like rearranging the cage and including new toys, removing nooks, nests and hidey spaces.
Neither one likes fruit but love romaine lettuce,
I have read many folks with cockatiels say their birds are not into fruit as much as they are vegetables. Maybe try some green peppers, peas, carrots etc