Hi,
Unfortunately this is not the best situation. The problem is they are already nesting, and if you change anything at this point, they will probably abandon the eggs, or if they have hatched, abandon the chicks. The chicks may or may not survive without being in a nest box. The parents will have trouble keeping them all together, and if one gets separated during the night, it will die without heat from the parents. The parents may not even stay on the eggs the entire time because they are so exposed. The best thing to do is give them plenty of privacy and hope for the best. Cockatiels have been known to incubate eggs and raise chicks in strange places, so with any luck they will be successful here.
Another problem is now the entire cage is their nest box. Whether they manage to hatch and raise these chicks or not, the pair has to be rested once the eggs are gone or once the chicks have been weaned. You will need to make changes to discourage them from nesting again right away. A Cockatiel in captivity will literally keep laying eggs until she dies from laying eggs too often. So when this clutch is done, this will be the time to make changes. Move the cage, rearrange toys, cover the cage early in the evening so they only get 8-10 hours of light each day, and stop feeding a lot of fresh food for a while. Keep moving the cage every time you notice her trying to settle down and nest again. After 6 months, give them a nest box. If she lays an egg on the cage floor, move it to the box. Usually she will figure things out if you keep moving the eggs.
Thank you for asking Lafeber,
Brenda