You take it from the Ramayana, each of the four brothers, Ram, Bharat, Lakshman, and Shatrughan, were ready to give up the throne and life for each other. Though they were stepbrothers, they co-operated with each other.
If you take it from the Mahabharata, Pandavas and Kauravas were ready to kill each other, and that leads the whole epic to the war of Kurukshetra and killing almost entire Kuru clan.
In both the epics, the elders were equally responsible. It was the main character that made the difference. Ram and his siblings choose not to rival each other, and they prospered, unlike Pandavas and Kauravas.
If you choose not to rival anyone, no one can make them your rivals. It can be your sibling or a competitor. Instead, if you decide to co-operate, everyone can grow to a better future.
The matter of rivalry is the question of choice. It’s up to us if we want to see foes around or want to make friends.