Ok this is kinda long hehe...
We had a "breeding pair" of quakers that was given to us. We figured out they were both females. One was semi friendly and would come to the front of the cage and talk to you (but still try to bite), and the other would run to the back and act very mean. Well, since they were not a breeding pair we decided to try to tame them. The one had been handfed (had to give her meds once and she obviously knew what a syringe was) and took to a friend of ours very quickly. She lets her do anything to her. It was amazing as they hadn't been handled in well over 2 years. The other female is slowly coming around. Once we got them in separate cages the "wild" female was MUCH more receptive to us. I'm sure she missed her friend and wanted attention. She will now come to the front of the cage and talk to us and bob her head and we give her cherios by hand. She says "want a cracker" and runs to the front of the cage. We have started stick training her so she can get out of her cage and she will step up on the stick to get out and be put back in her cage. She doesn't try to bite us as much and is getting used to us being in her cage to give her food and such. We are in NO WAY far enough along to get close to her getting on our hand or touching her, but her quality of life is much better now and she seems happier. She also doesn't scream as much as she is used to us moving around her (they were in an outside cage before).
All in all what I can tell you is it will take a LONG time. We have had Winter (quaker) now for a year, and I feel we have made great progress during that time. It can take several years for them to trust you. Just create a routine, stick to it, talk to them a lot. Once they get used to you being near their cage try offering treats. Once they get used to that maybe try stick training (with wings clipped). Just take each step slowly and make sure they are confident before moving on to the next one. Putting them in separate cages will probably shorten the taming process by about half. They also need to know you're not scared of them. They can sense fear. Persistence and patience will pay off. Hope that helps...good luck.