Question about conure bonding?

Hi everyone, i have two green check conures that I got two years ago. since then I have been working with them and training them every single day, by now they know many tricks and games but they still don’t seem bonded to me... the male, Loki is jumpy and afraid of any new objects... he bites often and draws blood seemingly without warning. I have tried to read his body language for signs of this behavior but he really doesn’t seem to show any. He is very cage territorial as well. I have been working on his issues for the two years since I got him and while he has come far and doesn’t bite as often, he is still afraid and definitely isn’t bonded to me. The female, Olive, is very sweet on the other hand. She loves to do tricks and never bites, but she still prefers Loki’s company over mine even though he sometimes bites her too. She will spend time with me but only when coaxed... I have been working on getting her to let me pet her head for two years trying all different tactics but she still seems to be holding back. I’m just at a loss atm because I’ve tried so many things and although she’s great and I absolutely adore her it seems like she always prefers Loki’s company to mine. And I cannot seem to reach a deeper more loving bond with her, I feel like I’ve hit a plateau. Any advice or new suggestions would be so appreciated. Thanks!
Ps: sorry for the super long post lol