It is very possible he was a wild caught, and they do tend to be a little more, well, wild than hand reared babies. A band could have been removed at any point in the birds life, and you would never know the difference. One of my moms zons is a wild caught, and despite having her for 40+ years, she is fiercely independent and definitely demands her respect

It's hard to put your finger on, but her behavior, vocalizations, even the way she flies is just different than a domestically raised bird. She is handleable by people she knows and trusts and does follow basic commands like stepping up. For the most part though, she does her own thing and doesn't want to take orders from people (much of that is my mom allowing her to because she is not a destructive or particularly aggressive bird). It's a very stark comparison to her lifelong "mate" (never produced chicks, but have been a bonded pair for 40 years) whom my parents got as an unweaned baby and was always a pet. He has the same freedom she does, but he's much more reliant on people. He'll go to anyone, is super friendly and has never bit. Wild caughts are aging and becoming rarer, but there really is a difference in behavior many parrot people haven't experienced.
Another trait of amazons is they do tend to bond to one person, and a lot of work has to be done to socialize them to go to other people they see and interact with regularly. You get into even MORE work if you want them to go to strangers. And unless you've had them since they were very young, they do tend to make you EARN their trust and love. It sounds like this bird was bonded to your grandma and now that she is gone, has began bonding to your mom. Anyone else who wants to be his "friend" is going to have to put in a lot of time and effort building trust, and unfortunately, living far away your not really going to have the ability right now. People living in the house can offer treats to build trust and work with the bird AWAY from his cage until a better relationship is built. Kind of work backwards with him- work on stepping up away from the cage, and once he's proficient, work on stepping up off the cage, and once he proficient, work on stepping up from inside the cage. That could take months and months of daily training sessions to reach that point. The bird can also be included in family activities by bringing him around in a small cage OR (preferably) a t-perch. Amazons are social, and he would probably enjoy being able to watch tv or eat at the table with your family

The more included a bird feels in their "flock", the better! And if old George, at this stage in life, doesn't magically want to become a cuddle bug, I almost say let him be and come around to whom he wants. Is he receiving appropriate care (diet/exercise/toys ect...)? Is he happy with his routine? Does he feel included? Does he understand he is loved? THOSE are the most important points. Best of luck.