Welcome back! Do these birds share a cage? As well, do you know if they are male or female?

Birds are like people...each of us/them have our own personalities. Even within the same family.
Both birds sound like they are doing very well with you. You can do more specific training by taking one at a time in a different, smaller room like a bathroom. By training, I mean handling it and getting it used to you. Use treats and keep the time short. No more than 10 to 15 minutes at a time and only once or twice a day. When they are out together, they may have less motivation to interact with you.

I am so sorry to hear about Boo. These little critters leave a hole in our hearts when they pass.