Is it permissible for the eldest son to withhold inheritance from his mother who is ill with doubt and selfishness, and who lacks sufficient understanding to help her children, but is affectionate towards those who humor her?

It is not permissible to disinherit an heir from their right, and whoever does so transgresses the bounds of Allah. There is nothing that necessitates placing the mentioned mother under interdiction, as there is no madness, idiocy, senility, or foolishness. Even if foolishness were proven, placing her under interdiction would require a judge's ruling. The right of parents is great, and Allah has coupled it with His own right. Their ill-treatment of their children does not justify disobeying them or squandering their rights. Rather, Allah commanded kindness to them, even if they strive to make their children associate partners with Allah.