Is the husband's action of shunning his wife's mother and brother for over a year, on the pretext of their mingling and participation in a mixed graduation ceremony with musical instruments, and the graduation of a close relative from the police academy, and in application of the Hadith: "The first deficiency that affected the Children of Israel was that a man would meet another man and say: 'O you, fear Allah and abandon what you are doing, for it is not lawful for you.' Then he would meet him the next day and find him in the same state, yet that would not prevent him from being his eater, drinker, and companion. When they did that, Allah struck the hearts of some of them with others," Islamically sound, knowing that he did not prevent his wife from visiting them?

Islamic law does not stipulate boycotting a disobedient person absolutely, but rather boycotting them during their act of disobedience, or if boycotting them leads to a benefit that is weighed according to the circumstances of the boycotter and the one being boycotted. This boycotting varies depending on the strength and weakness of those who boycott. If the benefit outweighs the harm, such as if boycotting leads to the weakening of evil, then it is legislated; otherwise, it is not. The hadith (definition) mentioned in the question has been weakened by scholars, and even if it were authentic, it does not imply absolute boycotting, but rather boycotting the disobedient person while they are engaged in their disobedience. It is not permissible for the husband to boycott his relatives for this duration merely for their participation in the celebration.