Well. Im not Sure about cockatiels. But when they are going to regurgitate they will have droopy wings and Bobbing there head. Etc. Um im sure someone else will help you on this subject Do you have them DNA'd ? If you suspect that one is a female i think you should seperate them from an unwanted litter as, Only experianced Breeders should be breeding etc. Or if your doing it purposly. But Cockatiel babys would be sweet.