It was the greatest feat of animal behaviour modification that I’ve ever achieved. When my roommate brought home a little kitten, I was able to train the cat to not eat/attack my cockatiel. So it IS possible. Now the humane society may not particularly approve of the “punishment techniques” that I employed to get the message through to the cat, but they were ultimately effective.
Even after I could see the cat understood the situation (and would still snag wild birds on a regular basis), I did my best to make sure I was always in the room when the two were out. But the ultimate proof of the training was when I came into my room to see my bird sleeping on the back of my chair, and the cat sleeping on the seat of the chair.
It was a long and stressful process. And I was dealing with a kitten, so that might have worked in my favor. If I were to make any recommendations, I would say “immediate punishment”. That is, the second you see the cat paying a little too much attention, you have to pounce and let him know he’s out of line. Squirt gun, flying lessons, and just tossing out of the room seemed to work. I think my personal favorite was solitary confinement - putting the cat in the bird’s cage. And then letting the bird walk around freely.
Budgie’s can be a lot of fun. They have a lot of personality. I would guess that all he’s been eating has been seed. Seed is pretty much candy for parrots - both as far as how much they like them, and as far as nutritional value. So for starters, transition your brother’s bird to pellets any pellet is better than seed). Also make sure he gets fresh fruits and veggies. You can still give some seed as a treat, but just make sure it isn’t what is making up the majority of his diet.
One thing many books don’t mention is that parrots require a good, solid (undisturbed) night’s sleep. Covering is good, but also make sure he’s in a quiet room) for at least 8 hours - 10 is even better.