Need to be a good Grass Leader. HELP!

Im still a bit unsure of my Grass team, I cant seem to figure out how to counter all my weaknesses. Ive made it into a drainer team using Leech Seeds, Giga Drain and poison type attacks. My team consists of Mega Venusaur, Rotom C, Breloom, Tropius, Ludicolo, and Ferrothorn. So if i could get some help that would be amazing!!!

Darklion, we need to know more about the team. Preferrably, we need to know the exact moves of each pokemon, their EV's, their items, etc. It's very hard to tell what's wrong with your team if you just give out the pokemon names. We need details~