Hi,
Because these birds are believed to be related, you need to keep them permanently separated. Related birds should never be allowed to breed. If any offspring survive, they will be genetically flawed and often plagued with health issues. They can have deformities and short lifespans. Many birds with genetic issues die within the first year. So nothing good comes out of related birds breeding. They do not know they are related and eventually they are likely to breed.
They will be much better pets when kept separate. Birds that share a cage will form a bond, even if they are the same sex, and eventually lose interest in being handled. It sounds like the male is wanting to breed, and he is being aggressive for a couple of reasons. If she isn’t receptive to him – and with her health issues she is unlikely to be receptive – he will get frustrated and start attacking her. He probably is biting you because he is torn – he wants to be a pet, but he also wants you to stay away from the female and her to stay away from you.
You can let them interact, supervised, outside of the cages, but really if each is tame to you when they are apart, it’s better for you to be a companion for each of them. The more time the female spends around the male, the more likely she is to start egg laying, and that brings a new set of problems. In captivity, female cockatiels are notorious chronic egg layers, and many end up needing hormone treatments to stop the egg laying, otherwise they eventually die from laying too many eggs. I’ll give you a list of things to do that can discourage egg laying.
To try to discourage egg laying:
Keep in mind that to lay eggs, she needs longer daylight, warmer weather, abundant food, and a quiet, private environment. The goal is to reverse these conditions.
Limit her light to 8-10 hours by covering the cage early each evening
Do not give her anything to use as a nest – no bird huts or tents, no box, bowl, etc. If she decides to sit in a food bowl, remove it and replace with smaller cups.
Do not give her anything to shred such as paper or cardboard.
Rearrange the toys in the cage frequently.
Move the cage to a different place in the room. Move the cage about once a week, or whenever she shows signs of nesting – settling on the cage floor for example. This disrupts her idea of having a stable place to lay eggs and raise chicks.
If you feed a lot of fresh foods, stop offering any for a couple of weeks, and then only offer them in small amounts about 2 or 3 times a week. You can resume normal feeding later when the birds aren’t being hormonal.
If she is let out of the cage, do not let her get in any dark cozy places and don’t give her free roam. When you let them roam around, this mimics searching for a nesting site.
When you handle her, limit any petting to only the head and neck – do not pet a bird on the body. Only a bonded mate is allowed to groom the body. We can’t be a mate, so touching the body is off limits.
If there is no metal floor grate, then do not use any bedding or paper in the cage tray – leave it bare and clean it daily.
Thank you for asking Lafeber,
Brenda