If you give them a nest box (or a tent or hut, any thing dark and cozy) they will breed. If you do not want to breed, don't give them a nest box. You can take away the eggs and refrigerate or freeze them and put them back, in this way she will sit them out for 20 days or so and give up. If you just take them away, without replacing them, she will keep laying which can leech the calcium from her body and maybe also lead to chronic egg laying (unhealthy for her).
It sounds to me like a typical first pair, they aren't sure what to do. He is right to go in the box some, but your hen is doing most of the work and that's okay.
Have you candled the eggs to see if they are fertile? Use a strong flashlight. If they have sat on them at least 5 days you will be able to tell. Here's
more information. Hopefully they are not fertile and you can do as I suggested with the eggs. I'm not sure where you live, I am in the US and there are so many cockatiels in shelters already that I would never breed mine. Breeding also shortens their life span considerably, and it is said that breeders do not make good pets, and pets do not make good breeders. So you have to sort of decide what you want.
Hope this helps. Good luck!