I think this is poppycock. There is no cosmic righteousness in slaughtering your relatives, or even your enemy, for that matter. I believe that the conflict that is the most well known part of the Gita is an allegory for the inner conflict within us. Our dharmic path, as you indicate, is our fundamental purpose. We must adhere to that path, even if it puts us at odds with others, including and particularly family members. Parents often have their idea of what path their children should take. The rebelliousness of youth is the effort to reclaim one’s own path. Paradoxically, this rebellion can cast one even further off one’s path. It can be a life’s work to realign with one’s dharma. I’ve seen this often, both as successes and failures.