My brother had adopted a baby boy 3 years ago, he is now 4. He is such a lovely kid, displays good manners, hugs all those who love him and entertains everybody funnily with his quotes from movies. But there's another side too. He is extremely aggressive and stubborn as an ox. His parents are having a hard time dealing with the kid and challenging their parenting skills. How can this behavior be changed, any advice please....?