When all your Pokemon are grass type, it's important to have team members that don't share too many weaknesses. Right now, you have 5 Pokemon weak to fire, 5 weak to ice, and 5 weak to flying, which is definitely a good reason to get rid of half the team. Especially since grass has so many weaknesses, you don't have room on your team for tanks; each of your Pokemon needs to either help cover the team's weaknesses (good Pokemon for this include Ferrothorn, Venusaur, and Cradily) or play some other unique and very useful role (good Pokemon for this include Breloom and Tapu Bulu).
