Use persuasion, rather than giving orders. No one wants to be bossed around. Family members, especially parents, tend to order family members around more than they do nonfamily employees. It is the familiarity thing again, or failure to appreciate the autonomous adulthood of children working in the company. Persuasion is the professional way of getting along with fellow workers, including family members.
Persuasion involves explanation of the rationale for something.
It is describing the desired outcome first. It is explaining the reasons for what is desired, the needs to be met, the importance of it all, the consequences of inaction and action. It is being clear about what needs to be done, while respecting the other's need to figure out how. It is listening for the other's viewpoints. It is seeking partners, not obedient servants.