Just leave them with the parents. They will be just as tame when you just finish the weaning process with them after they leave the nest naturally.
(So glad this b#llsh!t is illegal now overhere: no more 'death by amateurs' who think they can do a better job than the parents when there is absolutely no reason for it. And less psycologically scarring for the ones that actually do survive the manhandling.)
The other main issue is and reason not recommend, beside the time and work involve is? Hand-reared parrots of either sex may see humans as both potential mates and competitors. During the breeding season, and sometimes year-round, such birds can be very aggressive towards “mates” that do not respond appropriately (“appropriately” in parrot terms, that is!) and people who are viewed as competing for their “mate’s” attention. " Hence why you get a lot of parrots as they mature that are next to impossible to handle during mating season and severely bite people, or turn against owner." The good breeders let the parents raise them and just handle them for 30 minutes daily when they hit about 5 weeks old.
Plus such parrots are often poor breeders, failing to choose proper nesting sites or to feed their chicks appropriately. Some a lot of people don't even consider. I use to breed Cockatiels when younger.
It best just to let parent raise then at least as far as being fed and care for, even if they screw it up when younger and they end up killing the babies first time around? They usually get it the second time around. This is why most say wait around 18 months, or 2 years of age before letting them breed. They are less likely to screw it up and have health related issues.
Let the babies parrots be fed and cared for by their parents but then handled them on a daily basis as well. This is the ideal compromise between hand and parent-rearing. Fifteen to thirty minutes of handling daily, beginning when the chicks are 4-5 weeks old, has been shown to produce relatively tame birds.
The only reason I learned to hand raise at a young age when I was a kid was my first blue streaked lory was sold to us by a shady breeder that didn't fully complete the weaning process. So I had to do it and then a few Cockatiels that were rejected by parents over the years and my current male Cockatiel as he had a crop infection which they assume could be Cancer and original breeder was going to put him down. I had him now for about a year and 100% healthy.