What is the ruling on spending on a grandmother whose rich, stingy children do not provide for her, and instead give her from the Muslims' zakat through charitable organizations, and what is the ruling on taking zakat to spend on her, given that I am neither rich nor poor?

Wealthy children must spend on their poor mother. If they refuse, the wealthy grandchildren must spend on her if they have more than their essential needs. It is not permissible to spend on her from zakat funds as long as she is self-sufficient through the spending of her children or grandchildren.