Is a son considered sinful if he refrains from financially assisting his mother in order to give money to his brother's children, while he is more deserving of this money for his own children and personal expenses?

There is no sin upon you if you do not give your mother money she does not need, but apologize to her gently and kindly, and do not anger her. If she becomes angry, then it is better to give her what you can, without harming yourself or your family. Malik said: "I do not see that you should provoke her, but rather free yourself from her by whatever means you can." Know that investing money in usurious banks is forbidden.