I have and I strongly discourage you from doing this!! That is...unless you are willing to feed the babies every two hours or so around the clock for a couple of weeks! The chances of newly hatched cockatiels being successfully hand-raised are very slim. If you have a broody hen, by all means, let HER do the incubating and feeding the first couple of weeks. I forget how long they recommend letting the hen care for the babies before you can take them away and begin hand-feeding yourself. Google cockatiel care and I'm sure you'll find out. Also, the mother gives the babies certain antibodies you can't supply. I raised cockatiels for several years, before getting into chickens, and this is the best advice I can give you...don't do it!
P.S. WELCOME TO BYC