my cockatiel bonded pair had eggs, 3 babies hatched, they are now almost 18 months old. I was lucky they are very good parents. but, even with good parents keep in mind it is a lot of work and time for the owner. we stayed home most of time for about 1st 6 weeks after chicks hatched. things have to be kept very clean, we kept a close watch after babies were hatched, we kept a close eye on them. babies need to be kept warm, parents sit on them. the parents eat a lot when feeding the babies. what they eat goes to feed the babies and the parents. they went through a lot of millet spray, pellets, corn, peas as well as seeds. much more than fed normally. I remember at the time we had another pair of cockatiels. well, they just were curious, wanted to look at the eggs, and were more curious when the babies hatched. we ended up rehoming the pair that was curious, because the male of the pair that laid the eggs was going after the male of other pair, in mid flight even, fighting.I was afraid the dad would kill the other male. they were never living in same cage. then, the other pair started to lay eggs too, but the 1st pair, along with their babies when they got flighted, started to go into other pair's cage. the 2nd pair apparantly did not feel safe to lay eggs in their own cage, so she laid them in: a cabinet behind a glass door, the windowsill, and another cabinet. the male sat there, I asked him where his mate is, usually they point their head where another bird is, he just stood still, not moving. so keep this in mind, your other female can start to lay eggs even if she doesn't have a mate. and she could feel unsafe with the other pair around, especially if she's curious and just wants to look. Putting the other bird in another room would probably be a good idea, at least until the babies fledge. It seems once that happens I think they treat them more like any other bird. I don't know what would happen if their babies lay eggs. that has not happened, hope it doesn't. Our 1st pair, especially the male, was extremely protective and hormonal as far as the 2nd pair of birds goes. He normally is a real sweet friendly bird and has never been mean to any other bird. The mother bird has laid more eggs since but I replace them with fakes. One way I have found to tell if an egg is fertile is it is pinkish in color. It is a subtle color difference, but you can tell if it's next to something that is white. It is an unforgetable experience to raise baby birds, kind of a miracle really. they change day by day. growth rate is fast. their eyes have a film over them, like dogs do, at first and all cockatiel babies are born with yellow fuzz, which is down. they hold themselves up when standing by balancing themselves with their wing tips. they tip over sometimes, and then get back up. (we did not intend to breed, did not know eggs could be fertile, did not have a nest box), so we saw what was going on once they hatched. sometimes a baby got out from under the parent and just stood there. we would gently push the little one back by parent, who sat back on him. when first born they resemble a dinosaur, then their crop gets real big (if parents are feeding them well), it's one way to tell if baby is getting enough to eat, and their tummies are real fat. like little buddhas. then the parents start to feed them less, they get their feathers in, start to eat on their own gradually and slim down so they can fly. I hope this info is helpful. good luck to you.
