You sure did jump in with both feet! I rescued a B&G Macaw years ago that had been abused. Owners couldn't even handle her. She turned into an amazing companion. Sadly I lost her to kidney disease in 2020. I currently have a B&G Macaw, African Grey & a Umbrella Cockatoo.
I'd try frozen mixed veggies. Sweet potatoes cut in chunks (must be cooked) usually go over well. Once you get them eating mixed veggies you can add different ones & see what they like & will eat. The best pellet is the one they'll eat. Zuprem has a veggie flavor & also fruit flavor pellet. It may take time to get them to eat pellets if they never did before. A couple walnuts or almonds per day for the macaw. One for the Amazon & Grey.
My birds love Nutriberries. This site has them for "senior" birds, as well as pellets, etc.
Lafeber Senior Bird Nutri-Berries | Revival Animal Health
I'd suggest wet foods in the morning & dry foods at night. Remove wet foods/veggies/fruit after 2-3 hours as bacteria starts to grown then. Also you may need to eat or fake eat foods to show them they are safe to eat. You eat some & then offer them a bite. Make mmmm good sounds.
Parrots like silly, so sing dance, play upbeat music, etc. Explain everything to them. They like to know the what, why, where, etc., of everything. Example: you ask them to step up, so let them know why, lets go for a walk. Bird steps up, say good bird. You can use a small treat if needed.
The B&G lunging is because he is scared. It will take time for him to settle in, as everything in his world has changed. It may takes weeks or months. Just keep talking to him. Watch, listen & learn their movements & sounds. B&G macaws tend to be forgiving once you win their trust.
Macaws love to swing so if he does have a swing I'd suggest you get him one.