DashingScorpio makes a good point.
I would also add that when one duty clashes with another, the lesser duty, should give place to the higher duty. You will ask, "How do I know which is higher?" well, that which is more productive and on the side of the greater good.
The great warrior Bhisma fought on the side of the King. He was brought up in this household and was fiercely loyal. He knew, however, that Lord Krishna was fighting on the side of virtue, of righteousness. Yet he took the King's side.
Spiritual people say that when two duties clash, one should always take God's side. I've tried to explain this in the first paragragh, as aplied in a practical setting. Hope this helps.