Young nephew too mischievous

My nephew is 4 and he is hard to handle, he kicks and screams, hits and says “you are shit” asshole etc. the fault is not on the child but the parents. Anything he says or does is not corrected or disciplined but ignored. He’s coddled way too much. It has come to a point that he’s not much wanted around family because he’s behavior is unbearable. My 2 toddlers, 3 get kicked when he thinks no one is looking. In Daycare, he also has trouble making friends.

My husband is so fed up, he said next time when no one is going to open their mouths, he will. I’m not sure that’s a good idea, he says he doesn’t care anymore since his kids are involved and his sister isn’t being a parent. We don’t tolerate any bad behavior from our kids, it doesn’t matter that some think it’s just a phase, they’ll grow out of it.