Lovely bird's ( cockatiel's ) should rear their clutch without any trouble
Cockatiel chick's are quite ugly to start

but after a week or so they look much more like you expect
Give the adult's plenty of egg food , morning and evening maybe mixed with some soaked seed , the adult's will take plenty as soon as they get used to this .
If the days are short the evening feed should be supplied an hour before dusk to ensure the chick's get a bellyfull before the adult's roost for the night
Regards , Mick M.