I think working through your guys trust issues should be first.
Its always so frustrating to start where you are. And its hard to guide from afar. Because its such an individual fluid thing reading them and adjusting.
But they are so socially driven , they crave the connections with flock( you guys) . Green cheeks are vulnerable to flattery ( like all parrots but even more so I think!) They also can be bribed. And they are so smart and curious and want to be evolved in everything. So those are all things you. An use to your advantage.
Even after years of loving relationships, some parrots and fir sure my green cheek can develop sudden fear if hands or loss of trust. sometimes for known or unknown reasons. I've had to bribe and earn back my girls trust. We had a brief time of her charging and bite me and otherwise wanting nothing to do with me. I had a big conversation with her apologized ( something does get across) then I started going and giving a seed and bragging on her when she took . ( like 50 times a day) I talked and explained stuff to her. We got back to her being a sweetheart.
Really try to have a routine and ritual. Use the same words and phrases to explain things. Make sure to make a special time fir them when first wake up and before bed. Always go and say hello and give treat when you return home always go and tell them you are leaving and give a treat. Those seem simple but they go a long way in a birds world.
Shape behavior. Moving towards you for a treat. Shape behavior in small steps. Move out if cage to a perch attached on the outside for a treat. Then ask them to go to tge top of the cage for a treat , while you clean and change food. Lots if verbally praise as well.
I have some more links I will add thst might be helpful.
I like this one, because mistakes are made, adjustments, its good at showing the process, and importance of keeping sessions short and sweet
This is also a great article, kinda gets you inside how burds think . Observations, take time to do objective observation of the bird. Make nice of situations around bites. Video interactions so you can go back and look for non verbal cues you may have missed. Also talks about the importance of rituals and routine
To put it bluntly, keeping companion parrots is similar to trying to pound a square peg into a round hole. The fact that they do as well as they do is testimony more to their adaptability than it is to our husbandry efforts.
lafeber.com