Is the husband considered sinful if he disobeys his father, who refuses to let him work outside the family pharmacy and does not pay him a fixed wage, while he is in need of his own money to meet his family's needs?

If the husband's father prevents him from working elsewhere to earn a living because he does not pay him a suitable salary for his work, then he has no right to do so, as it harms his son and restricts him. Obedience to parents is in matters that do not harm the child, as mentioned by Ibn Taymiyyah and Al-Haytami. Therefore, the husband has the right to leave work with his father and work elsewhere, while needing to continue honoring his father, treating him kindly, and obeying him in what is good. The wife should assist him in this. The father's satisfaction is one of the reasons for entering Paradise.