I feel happy with many comments and advice here asking that the woman should be taken to the hospital. Indeed, it shows that Nigerians are gradually getting educated on mental illness.
Sadly, this is my story. Wife is refusing treatment, her family hid it from me but yes, I can't simply divorce her. Not because of any marital oath but simply because taking care of her is the right thing to do. The tragedy is that those taking care of the sick person are at the risk of losing themselves, I got help on time, so I am still coping some bit. It has altered everything I know about life and I am unhappy most times.
Please continue to support your brother to care for his wife. Stay close to him so he can also take care of the kids, he must find recreation and go on holidays at least once a year. He must focus on himself a lot otherwise he can't help his wife a bit.
He should forget his in-laws and not bother with them at all, otherwise he will be bitter and angry the more. He needs only positive thoughts all the time.
Not an easy journey but he will be good once the wife accept treatment and stays on prescribed drugs at all times. It is not a death sentence, nobody would know anything is wrong at the end of the day.
