I bought a pair of opposite gender birds from different stores, both "big box store birds" who were definitely not hand raised, they were both terrified of my hands at first, and they had every right to be. We are hundreds or maybe even a thousand times bigger than they are, are not birds, have an undeniably predatory look about us, and we have a compulsive need to stuff out giant hands (also many times larger than parakeets) into what they consider a "safe" place.
Be gentle and willing to take time with them, it is true they may never come around, but in my experience, that is incredibly unlikely. They are already willing to eat from a millet sprig you are holding, that's pretty big whether or not it seems to be, let them go at a pace they dictate, your rewards are going to be poop covered hands, and some 10 to 15 years of servitude to a couple of feathery buttheads absolutely deserving of the heart they will steal (if they haven't already) and you'll enjoy every bit of the shenanigans they get themselves into.