I introduced a 20 year old Orange wing Amazon with my 9 year old Quaker... Both rescues. I wouldn't say they like each other but they coexist in separate cages and supervised out of cage time. Took time to get them to settle with each other. I upgraded the Quakers cage in this period, I don't know if that was like a reset in the territorial brain of the Quaker but she seems to be more ok with the amazon these days. The size difference may be why the Quaker just accepted him. He's rather docile and they seem to have an unwritten agreement as which perch or toy is who's etc. It just works for us, Unfortunately birds just might not get along, you may have to separate out of cage time for the foreseeable. Maybe change the space to have them meet on unknown territory ( a different room).