Poll question: Do you ever wanna give someone parenting skills but you don't you just keep your mouth shut?

My brothers been in and out of his sons life and he's only five years old. He has like no discipline whatsoever ever and he's a spoiled brat. He was mostly raised by my brother's girlfriend's parents. They handed everything over to him. He throws tandrums just to get his way. Well my brother finally has his life together after so long and he's staying with us. When he has his son over he just doesn't listen and it's so frustrating. And sometimes my brother will just let it go.