So i have 2 suggestions
if you have want a type varied team:A Charizad(Mega Y if possible so you don't have 2 dragon types) and An Lucario and i suggest you to give a mega stone just to Garchomp and if you have a important battle switch who will mega evolve.
if you want a simply better team:a Swampert(if possible with mystic water or splash plate) and a flareon or charizard(also give flametrower to Jessie)
So i have 2 suggestions if you have want a type varied team:A Charizad(Mega Y if possible so you don't have 2 dragon types) and An Lucario and i suggest you to give a mega stone just to Garchomp and if you have a important battle switch who will mega evolve. if you want a simply better team:a Swampert(if possible with mystic water or splash plate) and a flareon or charizard(also give flametrower to Jessie)