Yes what a difference a year can make and it shows, we have always preached taking your time and using much patience when dealing with greys especially rehomed ones, a relationship cannot be rushed for to get them to trust us it takes hours, days, weeks, months and sometimes even years to gain that trust but its worth it as you now know. Does the rest of the family have any interest in becoming friends with Motu? They should stay a distance away so he does not growl and talk to him, maybe offer him a treat, he may never come to allow them to touch him but they can still interact with him and maybe one day he won't be growling at them either. Greys do tend to pick favorites, my grey prefers me but she is allowing my hubby to interact more with her than she used to, it just takes time and the important thing is not to force themselves on him, let him come to them in his own time on his terms.
One thing I want to mention is the cage he is in seems small to me, too small for a Cag, it would be so much better for him if he had a bigger cage that he could open his wings and flap without touching the sides, its important they have enough room to play and reside in when they do spend time in them.