Is it permissible to prevent the mother from giving to the sister from the son's private money, knowing that the mother disposes of the son's money without his knowledge, mistreats his wife, and the son's financial situation is average?

The mother is not permitted to take from her son's wealth without his consent and her need. The son has the right to prevent her from giving his money to his sister. Although the Hanbalis hold that the father may take from his son's wealth without need, provided he does not cause detriment to the son's wealth or give it to another child. The son should treat his mother with gentleness and kindness, without offending her, and it is preferable for him to give her what does not harm him.