Marriland

Celebi @ Leftovers
Trait: Natural Cure
EVs: 252 SAtk / 4 HP / 252 Spd
Modest Nature
- Nasty Plot
- Giga Drain
- Earth Power
- Hidden Power [Ice]

Special sweeper. Switch in on a favorable move to get a Nasty Plot setup and let the sweep begin. Giga drain as STAB / Self heal, Earth Power for Fire/Steel Types, and HP Ice for Dragons and Grass. 

Infernape @ Life Orb
Trait: Iron Fist
EVs: 4 HP / 252 Atk / 252 Spd
- U-turn
- Overheat
- Mach Punch
- Stone Edge

Mixed attacker. U-Turn for scouting, Mach Punch for quick-hitting fighting STAB, and Stone Edge for coverage vs dragons/flying. Overheat as a fire STAB sacrifices SpAttk without hurting other moves. 

Latios (M) @ Expert Belt
Trait: Levitate
EVs: 252 Spd / 252 SAtk / 4 HP
Timid Nature
- Draco Meteor
- Psyshock
- Surf
- Thunderbolt

Second special sweeper. Good coverage, two STABS, and Surf and Thunderbolt add OHKOs to some that others can't handle.

Espeon @ Light Clay
Trait: Magic Bounce
EVs: 252 Spd / 252 HP / 4 SAtk
Timid Nature
- Reflect
- Light Screen
- Wish
- Hidden Power [Fire]

Support #1. Switch in on entry hazards and set up dual screens. Wish for healing, although it's kind of weak from Espeon. HP Fire takes out common entry hazard users (Ferrothorn and Forretress)

Gliscor @ Toxic Orb
Trait: Poison Heal
EVs: 184 Def / 252 HP / 72 Spd
Impish Nature
- Substitute
- Protect
- Toxic
- Night Slash

Support #2: Toxic and Sub/Pro to annoy opponents. I took out the more common Earthquake / Ice Fang because I have them on others, and needed something to hit Alakazam/Reinucleus hard. 

Gastrodon @ Leftovers
Trait: Storm Drain
EVs: 84 Def / 252 HP / 172 SDef
Sassy Nature
- Earthquake
- Scald
- Recover
- Toxic

 Support #3: Walls a lot of threats and hits back with Scald/Earthquake. Scald adds possible burn support but Toxic is preferred for damage. Recover out of necessity. 

#1 Ninjask @Focus Sash

#1 Politoed @Choice Specs

First, I assume this is B/W2 since you didn't say. Second, I assume you are building around a lower tier (NU/RU?). That said:

My comments on the three you have: 

Rampardos: I would give him Crunch instead of Pursuit; save Pursuit for a pokemon that will get a STAB off it.

Charizard: Well, I would get rid of Dragon tail for two reasons. First, its damage is only super effective against other dragons, so it's not useful for damage. Second, its phazing ability is a very low priority. With Charizard's mediocre defenses, he can easily be KO'd before you get a chance to make use of it. Trade Air Slash for Sunny Day and your defensive move for Solarbeam. With Charizard's DW Ability, its SpAtk is boosted in the Sun. This will make for a nice sweeper.

Umbreon: Although an excellent supporter, I wouldn't try to have him fill two roles: utilizing both Heal Bell and Wish can do more damage than good-- pick one or the other. Wish is probably a better alternative because your opponent will be hesitant to his Umbreon with a status effect due to its ability Synchronize. You can fill the last spot with a status inducing move like Toxic, but keep in mind this opens your opponent up to paralyze, burn, or poison Umbreon without fear of having their Pokemon affected, too. 

Now, Pokemon you might consider for the rest of your team:

Your current setup with just these three has two major weaknesses: Both Rampardos and Charizard are weak against Water, and both Rampardos and Umbreon are weak against Fighting. With the exception of Umbreon, none of your pokemon have superb defenses to guard against an unfavorable switch-in or Hidden Power. 

To guard against a devastating Water-type attack that could KO either Rampardos or Charizard, you could add a Pokemon with the ability Water Absorb. If you correctly anticipate a water attack, you can switch-in your Water Absorb pokemon and completely block the attack (and, if the Water Absorber is damage, heal them a bit, too).

Vaporeon or Jellicent are both good choices thanks to their defenses. Jellicent is probably the preferred choice, because its Ghost typing allows it to also block incoming fighting-type attacks aimed at Umbreon or Rampardos, essentially covering both of your weaknesses in one shot. Make a defensive Jellicent with Leftovers, and give him Recover, Protect/Taunt, and a status-inducing moves like Toxic coupled with a STAB such as Surf, or consolidate the two with Scald and add a fourth move like Shadow Ball or Hidden Power. 

Whether you choose to add Vaporeon or Jellicent, you are opening yourself up for a weakness to Thunder attacks that will hit both the Water-absorber and Charizard for a lot of damage. A multi-type Ground Pokemon like Flygon is a good addition here, able to block the thunder attacks (and Earth attacks thanks to Levitate) and give your team some much needed STAB coverage in Earthquake and Outrage. You could also give Flygon U-Turn to escape Ice-users (and do some good damage to UU Ice-types such as Abomasnow and Weavile). Fill the fourth spot with a physical Fire Punch or Stone Edge. 

Finally, you are missing the ever-present Steel types and all of their glorious resistances. Dual Screen Bronzong could be a good choice thanks to its excellent defenses and immunity to Ground-type attacks, but may not be necessary with Umbreon as support. If you want another offensive-type instead, Bisharp is a good choice with only three major weaknesses (Fire, Earth, and Fighting), twoof which you can block by switching in Jellicent and the other by switching in Flygon. This would also provide you with immunity to Psychic- and Poison-type moves, especially Toxic/Toxic spikes, not to mention less damage from Stealth Rocks. 

Alternatively, you may want a different support to fill the last spot with Rapid Spin. Starmie provides good offensive support, but Forrestress gives you both Rapid Spin and entry hazards. 

Hope this helps. 

Added my sixth =P

#1 Ferrothorn @Leftovers

Too bad most evasion-enhancing moves are typically banned in competitive play...

1. Swampert is better suited for physical attacks. Replace Surf with Waterfall and Ice Beam with Avalance (which deals double damage if he is hit first before using it). 

2. If you're using Excadrill with Sand Rush, you should have some way to set up sand storm on your team. 

3. I would give Bronzong a STAB attack instead of Rock Slide. Given his slow speed, you could try Gyro Ball, but since you're setting up Trick Room maybe not.

4. A well-built Scizor would do your team a lot of harm, having only one weakness (Fire), which none of your Pokemon are able to counter. Likewise, you have no Grass-type attack to counter the common Water/Earth-types. Give Starmie or Bronzong Energy Ball. 

5. You would also be in big trouble if your opponent opened up with Ferrothorn (which I always do), who is a perfect counter for Swampert and Ninjask, your first two Pokemon. You have no Special Fighting/Fire attacks to get rid of it. Power Whip would OHKO Swampert, Gyro Ball would OHKO Ninjask. Add Ingrain/Leech Seed + Leftovers and Toxic Spikes, and its ability Iron Barbs, and you can see how your team could be whittled down by just this one massive tank. 

6. Given the above, take away Curse and Crunch from Snorlax and give him Brick Break or Fire Punch and Sleep Talk. You can counter Ghost types with Starmie using Shadow Ball instead.