Is it permissible for children to take usurious interest from their elderly mother's bank account to cover her expenses in a nursing home and to make up for the deficit in her pension, knowing that the mother considers this interest permissible based on a fatwa attributed to the Mufti of Egypt?

It is not permissible for children to take the usurious increment and spend it on their mother, because it is unlawful and must be disposed of by spending it on the welfare of Muslims. Even if the mother follows someone who permits it, it is not permissible for the children to spend from it while they believe it to be unlawful.