So there are a couple points of optimization:
items:
Garchomp:
scarf, soft sand or dragon tusk are good items. Each
Meowscarada:
hyper offense + focus sash has good synergy with the overgrown ability. (Shell bell doesn’t do much for an offensive mon)
Kangaskan:
you could give her the mega stone. Mega kan is pretty solid in matchups which your charizard is bad in.
Sneasler:
Mental herb to counter intimidate works well
Moves:
in general your move selection is suboptimal. A clear example of that is that 0 mons run protect. I personally run protect on at least half my mons, but even running it on all of them can be good for a beginner player.
As for the moves I’ll list the most popular sets below for the mons which look the most suboptimal.
Garchomp:
earthquake
Dragon claw
Rock slide
Kangaskhan:
fake out
Drain punch
Sucker punch
(I forgot the name. But the most powerful normal type move with the recoil dmg)
Ev’s:
atm you didn’t share your ev’s, so I don’t know if you have any suboptimal choices there.