What is the ruling on the brother who caused the death of his younger brother after bringing his brother-in-law to fight with his siblings? And is he disinherited? And what should the family do regarding this brother and his wife who incites problems?

Your brother has no right to inheritance due to the presence of the father, for a brother does not inherit when the father is alive. If he were the killer, that would also prevent him from inheriting, according to the saying of the Prophet, peace and blessings be upon him: "There is nothing for the killer from the inheritance." However, merely bringing the killer does not make him a killer. What your brother did by severing ties with his father and causing his brother's death is considered cutting off kinship ties, but it is not permissible to boycott him; rather, it is obligatory to maintain ties with him as much as possible.