to gain mass what would be the best training method and diet to follow.
i was thinking of west side for skinny bastards with The-get big diet for bodybuilders both of this site\
Quite simple–
lift big–eat big
I know you want the magic system, but bottom line, different systems work better for different people.
You could use any cobination of any mass building diet and mass building lifting scheme and achieve different results than your brother. Use maximal weights with lower reps as your base. Periodize in higher reps with lower weights to give your body a little break and different stimuli. But the goal here would be to focus heavy and increase steadily the volume.
Nutrition is as/or more important in combination with the workout. Maximizing parameters and potential of intake could really speed up your goal process.
You got it right with the diet. The only thing I would advise is that you don’t stay on one program longer than the article recommends.And when you switch - ALWAYS switch to one that has you training more, not less. Every month on the last week, cut your weight in half and just do light workouts that you feel you can repeat twice, but you don’t - it’s a week to relax and eat to let the growth really settle in.