[@NightmareInd] Instead of starting at the end of their journeys we can start at the beginning where they form the bonds with their pokemon and the rivalry between the 2 and friendship forming
Ideas:
Some rival battles
Maybe not just gyms, maybe contests 
Maybe we could have where they have a pokemon each from the same evolution line where it is a split one and argue which one is better
Mayb the older one, as well as being a rival can be a bit encouraging through the rivalry and, unknown to the older one, the older one's words helped the younger one through their journey
Maybe they are confused near the time of the league and find a way to express themselves but not to each other
Maybe with the starters, they get contrasting types