Doubts problem

I have an elder brother who is very pious and religious person. But from few days he's caught up in doubts during ghusal. He's bathing for more than 3 hours. He's continuously washing hands for hours. My parents are worried. He's missing prayers frequently and even he's breaking his cleanliness during the nights. He's a very good boy who is not involved in any affairs. He even used to sit for i'tikaaf in Ramadhaan. I request you to give me helpful advice. And also let me know what's the reason behind this.