What is the interpretation of what is happening to my brother and his wife, involving strange abilities and spiritual claims? Is it permissible to boycott them to avoid discord and protect the religion, knowing that they do not pray and claim that jinn pray on their behalf?

If what was mentioned about the Moroccan man and the brother's wife is true, then know that they are sorcerers who deal with jinn and devils. All their claims about the necessity of obeying them, or their connection to angels, or messages from the bearers of the Throne, or that abandoning prayer is a sign of God's love for them—all of that is a clear lie and grave misguidance. The duty is to advise them and remind them of God. If they refuse, then cut ties with them and boycott them for the sake of God. There is no sin in boycotting people of misguidance. The boycotting that is forbidden after three days pertains to worldly disputes, but boycotting sorcerers who are infidels is permissible without restriction.