Is the son's disobedience to his father – who insists on giving money to the unemployed and debt-ridden son – considered an act of disobedience (uquq), given the son's belief that his brother's best interest lies in not giving him money so that he takes responsibility for his actions?

If the son's welfare lies in withholding money from him due to his recklessness, squandering of wealth, and unjustified idleness, then you bear no sin in disobeying your father by not giving it to him, and this is not considered an act of disobedience. It is recommended that you speak to your father gently and explain to him the benefit of not giving your brother money, and that you are not being stingy with him, but rather seek his reform. Likewise, your brother should be advised and made aware of the error of his ways, and that withholding assistance from him is for his own good.