For starters they are probably scared out of their minds and need some time to adjust. Please give them at least a couple of weeks before pushing it if hey are already showing such extreme signs of fear. Remember, cockatiels are prey animals, not predators. 90% of bites a re fear driven, and the rest are learned when humans don't respect the bird.
AFTER you have given them enough time to properly settle in, at LEAST a couple of weeks, if she still is lunging through the cage bars I suggest switching her to a new cage, but only when you know you will have time to get her out of the cage and really work with her at least a couple of times a day. Another thing that helps is to remember; NEVER CHASE YOUR BIRD AROUND THE CAGE. Unless the house is on fire or there is some similar emergency, chasing your bird around to catch them ruins trust, don't do it. You need to be patient and come to them with respect and understanding.
I have learned that often a bird has been forced by human hands will accept a perch. I have one bird who I NEVER put my hands inside her cage while she is in it. I always wait for her to come out on her own, or offer her a perch. She was abused by hear last owner, and will rip a hole in me if I reach in there. She readily accepts the perch however, and happily steps from perch to hand as soon as she is outside the cage. Remember to be POLITE with the perch. This is not your excuse to go pushing on her belly trying to get her to step up. Offer treats, entice, never force. Cockatiels are sweet, generally mild mannered birds and forcing is not necessary or fair.
