In my personal experience, grays are very hard to make bond with another bird, even another gray and even with a sibling. I had a brother and sister that were raised and lived together their entire 8 years staying with me for 9 months and they completely ignored one another.
Yes, you need to change the diet asap.
As to his name, I would use the first one he got because that is usually the name they recognize as their own. I got a Yellow Nape Amazon from his second owner, he had changed his original name, Zeus, to Oscar but I call him Zeus and, although he never did react for a couple of years to it (he had been abused by his second owner and had severe aggression issues from it), once he started feeling more like himself, he did and, now, he comes when I call him.




