Is the mother sinful if she refuses to divide the land in which the children shared, despite the customary council's ruling to divide it?

It is not possible to definitively state that the mother is sinful in this case, due to a lack of knowledge regarding the details and justifications. However, generally speaking, it is not permissible for anyone to come between a person and their right to benefit from their property. Whoever does so is a usurper (ghasib). Usurpation occurs by establishing the hand of the usurper and removing the hand of the owner, and it is forbidden by the Qur'an, Sunnah, and consensus (ijma'). Allah Almighty says: {O you who have believed, do not consume one another's wealth unjustly but only [in lawful] trade by mutual consent} (Quran 4:29), and because the Prophet, peace and blessings be upon him, said: "The wealth of a Muslim is not lawful except by his willing consent."