there will be no eggs until its time to lay a new one, and they can make up a new location where eggs would be, right? She will have to lay it somewhere if she s already producing it.
Is it possible that parents become violent to the babies due to this changes? Or, can she have an egg binding due to stress? Is it better to remove the nest cage at all out of sight or let them in to inspect there is no nest box? Right now they are all flying around chirping like crazy.

What would you personally do, Carolyn? I feel like a person removing a newborn from a mom who is hormonal. I wouldn't like it to be done to me...
At least, I won't be afraid to candle eggs in the future. Right now the box is getting cleaned a bit. The new egg is resting wrapped in napkin. The cage is empty and locked still at the same place.

By the way, does it mean anything that there were no fertile eggs in the second clutch? Male is getting tired maybe?

I don't know what happened to the second clutch. The male is obviously fertile since the first clutch hatched successfully.

If the hen already has a second egg "in production" (which is likely) she will have to lay it somewhere, even if that means standing on a perch and dropping it on the floor. But this does not mean that the egg will be laid in a place where she is willing to nest, and if she is unwilling to nest in that place she will abandon the egg.

Hens don't get sentimental about lost eggs, or at least they don't think about them for very long. Sometimes confiscating the eggs is the right thing to do, and I don't hesitate to do it. Your adult birds were not perfect parents to their first clutch and you had to intervene, which was difficult for you and for the chicks. Do you think it's worthwhile to go through that again if necessary? Are you confident that you can find good homes for another clutch? If not, then it's OK to yank the eggs. The parent birds won't be thrilled about it but they'll get over it quickly and will be happy again soon.

I am thankful that I had relatively little trouble, only when they started the second clutch and reduced feeding the chicks. I think they are great parents for the first time.
ABout not being sure finding good homes - I agree.

What is naturally the breeding schedule? Spring and early fall?

How long the chicks are considered "babies" for selling?

If she stops laying after the second egg, we are good. How many eggs would indicate she needs nestbox back?

Cockatiels are considered to be babies until they're a year old.

Cockatiels are opportunistic breeders, meaning that they don't have an official breeding season and will breed whenever conditions are favorable. In our comfy homes that can mean all year long, and many cockatiels will produce clutch after clutch unless something is done to stop them. This is not healthy for the parent birds. Cockatiels do tend to be more intent on breeding in the spring since that's the time of year that's usually most favorable for breeding in the wild. So that's usually the time of year when it's most difficult to prevent egg laying.

If this was my bird, I'd give up and give the nest back around the third or fourth egg. Hopefully she won't take it that far, but time will tell. If she goes for another clutch now, be sure to take action to prevent her from laying yet another clutch right after this one. Too much egg laying can ruin her health.

Would you give nestbox back right now?

We could prevent this one if I wasn't too scared to candle eggs so I wouldn't wait this long thinking it could still hatch.

If this was my bird I wouldn't want her to have another clutch right now, so I would take the nestbox away. But it's up to you to decide. If she had actually raised two clutches I would definitely advise that you prevent a third clutch. But she only actually raised one clutch, so her physical resources shouldn't be depleted as much.

yesterday I managed to get everybody into cages by 9pm. Cuddles, the hen, volunteered to go to her old cage, so did Trillie, the cock. The chicks spent a night by themselves in the new cage. But in the morning Trillie started his outraged song that he used to be doing sometimes in the past (but not while the nestbox was present). You know, when they chirp angry and wouldn't stop. So I will try to house him separately the next night.
They fly and chirp a lot since I removed the nest. I am afraid, chicks don't get a good chance to eat as parents startle them to fly. I would say, everybody being nervous.

Cuddles is checking the cupboards. I hope her next egg will be due when she is caged, in the morning. Otherwise, I may never find the egg.

The pearl girl is having a dark line on her beak, I can swear she didn't have it at the beginning. What could it be?
The father preens babies but they always end up screaming. Does it mean he hurts them, and if so, does he do it on purpose, I wonder?

Do people prefer to buy babies up to a certain age? Or, the older, the better? Would it be more difficult to sell them if I wait longer?