How do u level up your pokemon team togeather?

When i play pokemon from beginning, i always lvl up only my main pokemon and some other pokemon with xp-share. And then the problem is at the end when u only have 1 or 2 high lvl pokemon at the league. So i was wondering, how do u lvl up your pokemon team togeather so when u reach league u have all your pokemons like lvl 50. I dont really know how to so if someone can write a quick guide would be nice. Thanks.

The only way to equally train your Pokemon in these earlier games is to train them each in battle. In the newer games, like Pokemon OmegaRuby & AlphaSapphire, you can use the EXP Share for ALL of your Pokemon.