Keep trying and don't give up! Every budgie is different and it just takes time for them to fully muster up the courage to do something we want or what they want. Some budgies learn quick and are braver, others take time and are timid.
Giving them away to another home and letting them go I think will be completely unfair just because you think you're not doing a "good" job and that they are not going out of the cage. They may be very bonded with you and the thought of them being in another home will be tough on you and the birds (them getting used to another home and family again and getting stressed out).
I'm sure you're doing an absolutely amazing job and your budgies thank you - for giving them a happy and healthy life and for taking care of them. Don't beat yourself up and don't let yourself down.
I feel that way sometimes... Looking at my budgies and then telling myself that I'm not doing enough to make them happy... But in the end, and in reality, it's totally the opposite. Just us being there for them, feeding them, playing with them, talking to them and loving them is enough.
To encourage them more to come out, you can:
-place a bird playground near the cage with some toys and millet to try and get them to come out.
-place some toys, tree stands, perches outside the cage and just wait for them to come out or by placing them there.
-slowly taking them out while rewarding with millet and talking to them gently...
-or you can gradually train them to get used to the "outside-of-the-cage-world" while slowly getting them closer and closer to the cage door (so having them to step up, and gradually getting them closer to the open cage door. After they're comfortable being exactly at the cage door, you can then gradually take them out (getting slightly further and further) from the cage.