Aerodactyl @Leftovers
-Iron Head
-Aerial Ace
-Stone Edge
-Earthquake
Pressure, Jolly/Adamant
252 Atk, 252 Spd, 6 HP
I don't like Aerodactyl with all the Fangs and Iron Head. I just don't. This is a pretty basic physical sweeper. It has Leftovers for lack of anything else unless you wanna Band it or even Scarf it.
Toxicroak @Choice Scarf
-Cross Chop
-Stone Edge
-Earthquake
-X-Scissor/Poison Jab
Dry Skin, Adamant
252 HP, 252 Atk, 6 Spd
Another basic sweeper, blah blah blah. Were this Doubles, I would have recommended a SubPuncher, but it doesn't work as well in Singles, especially when he would have to set up his own Rain Dance. At least with Dry Skin you can take advantage of other Rain Dance teams and switch into attacks like Surf and Waterfall. That's always a plus. X-Scissor for coverage or Poison Jab for STAB, take your pick.
Swellow @Flame Orb
-Protect
-Facade
-U-Turn
-Brave Bird
Guts, Jolly
252 Atk, 252 Spd, 6 HP
Flame Orb is better on Guts because Guts ignores Flame Orb's Atk reduction and just gives you the 1.5x boost. Toxic Orb is for Pokemon running Quick Feet. U-Turn or Protect could maybe go for Pursuit. Another very basic and very obvious set up.
Mammoswine @Leftovers
-Curse
-Ice Shard
-Avalanche
-Earthquake
Snow Cloak, Adamant
252 HP, 252 Atk, 6 Def
This is what I see most other Mammoswine doing. Ask someone else, really, because I've never used one myself.
Magmortar @Power Herb
-Flamethrower
-Solarbeam
-Thunderbolt
-Psychic/Focus Blast
Flame Body, Timid/Modest
252 Sp.Atk, 252 Spd, 6 HP
No reason to have Solarbeam if you're not gonna have Power Herb to support it. Otherwise you're just asking for pain. Psychic hits a lot of types for neutral damage which is good, and Focus Blast is just Focus Blast... I'd go with Psychic, myself. This is your ONLY Sp.based Pokemon so far, mind you.
Venusaur @Leftovers/Black Sludge
-Leech Seed
-Sleep Powder
-Substitute
-Amnesia
Overgrow, Bold
252 HP, 252 Def, 6 Sp.Def
From crap sweeper to beastly wall. My EV spread is off, I know, but Sami can fix that quite happily. Sub-Seed, Amnesia. If they're sleeping, all the better to stall. Amnesia or Sub might wanna go for Giga Drain or Body Slam or something so you'll have a consistent attack. Body Slam has parahax, and Giga Drain restores your HP, but it's pretty weak. If you go Body Slam, make it an Impish nature.
After my changes, you have FOUR Phys.Sweepers, ONE Sp.Sweeper, and ONE Phys.Wall that could pass for a mixed wall after a couple Amnesias. I personally don't like to go without two walls, one Phys, one Sp, two Phys.Sweepers, and two Sp.Sweepers. It's very well rounded, and I normally have one or two of the sweepers with some utility attacks like Taunt, Sleep Powder, or T-Wave. The walls normally carry moves like Stealth Rock for me.
I say get a solid Sp.Wall for Aero or Toxicroak, kill off Aero or Croak for another Sp.Sweeer, and maybe get SOMEONE that can Taunt. Taunt wins games.