The correct amount of carbs is very individual. The glucose meter will help you with this, alongside a food diary.
Test immediately before eating
Test again 2 hours after first bite
Look at the difference between before and after
If the rise is 2mmol/l or more (preferably less), there are too many carbs in that meal for him
Record all this in the food diary and watch for patterns. His danger foods will soon show themselves.
It may be a question of reducing carb portion sizes, or it may be better to eliminate some altogether.
As for brown rice and pasta, they are just as carby as the white stuff, same with wholemeal bread. It just takes a bit longer to convert to glucose.
If he has low enough carbs and high enough fats he will not lose energy. It is a matter of balance and finding the right balance for him. The fewer carbs, the more fat is needed. He also needs plenty of protein. It is trial and error, but getting his blood glucose down is a priority.