What is the ruling of the Sharia regarding a man boycotting his sister and some of his siblings, and preventing his wife from communicating with them, claiming that his sister caused him harm, and mentioning examples of that, and how should one deal with them in a way that conforms to the Sharia?

Severing ties of kinship is a major sin, and one who severs these ties is threatened with a severe warning, for such a person will not enter Paradise. The wrongdoing of brothers does not justify severing ties with them. Rather, the one who truly maintains ties is he who connects with those who cut him off. The wife should advise her husband who severs his kinship ties and warn him of the dire consequences of this severance. She should strive to reconcile him with his brothers and improve their image in his eyes. If he has a usurped right, he may reclaim it through permissible means, but this does not justify severing ties. The wife should also keep the children away from this conflict and instill in their hearts respect for the rights of their paternal uncles.