Again, I read these posts with the advice given....there is only one way to avoid brake fade, slow down. Its simple, your brother is going downhill too fast. Brake fade happens because you are asking too much of your brakes, they are talking to you when you get fade, the penalty for not listening is death or injury to yourself and or others. Period.
Not being nasty, motorhomes are not cars and cannot be driven like cars, they reqire some education, just like driving a truck does. Slow down, at best you'll scare your pants off, at worst you'll lose brakes completely and kill someone.