If your brother is a little “fat” as you say, he probably is not eating well. So a change to a healthier diet will help him lose weight and that alone could help him move faster and jump higher. Jumping demands strong quadriceps and calf muscles. Doing squats are great ways to develop the quads. Tell him instead of walking up stairs to jump up them instead. Also find a wall where he can do vertical jumps and touch the wall. Put a piece of tape 2” higher than his highest touch and have him repeat jumping until he hits that tape and them move it up another 2”.
Diet and strength training will go a long way to him jumping higher. Here are jumping higher tips from a br />
basketball website
JUMPING EXERCISES
Deep Knee Bends—- Be standing. Slowly bend at the knees while keeping your back straight. Slowly crouch down as low as possible (it shouldn’t hurt) and slowly rise back up. Do this 15 times. Over time increase to 20, 30, etc.
Deep Knee Bend Jumps—- Be standing. Crouch down as described above but fairly quickly, almost touching your bottom to the ground, then explode upwards as high as you can. The moment you land, immediately crouch and launch back up again. Do this 15 times, and when you can, increase to 20, 30, etc.
Toe Raises—- Stand regularly, then raise up onto the tips of your toes. Lower back down. Don’t just rock up and down, do it slowly (not too slowly) but steadily. Repeat 30–50 times.
Toe-Raise with Weights—- If you have any sort of weights, holding/wearing them while doing these toe raises will help. Use small weights (a mere 5 or 10 pounds is fine) and work your way up.
Stomach Crunches—- We believe that sit-ups are bad for your back. Stomach crunches, where while lying on your back, using your ab muscles and keeping your back straight, you rise up just enough to lift your shoulders off the ground, are better. Do them often – perhaps for 10 minutes in the morning and 10 minutes at night.
Jumping Rope—- Jumping rope definitely helps your vertical leap. Jump rope while watching tv or something. Make it a habit.