Always give us your "dream team", at lvl 100 with items (if you don't know what items to give, just ask us but we ALWAYS expect lvl 100 teams), EV distribution (check out the faq in the instituition or in my sig if you don't know what's EV) and personality (which you did already). For Pokemon like Gardevoir, tell us which ability you're choosing.
Sceptile - "Gex"
*Modest*
Arial Ace
Leaf Blade
Mega Drain
Dragon Claw
Sceptile- modest @ chesto berry
EV: Spd and SpAtt
-Dragon Claw
-Crunch/protect
-Leaf Blade
-Rest/leech seed
Not that good of a moveset as you lack access to FRLG it seems... it's the best you can do for the time being... Use protect and leech seed combo if you want (if you got FRLG, replace protect with Sub)
Blaziken - "Helios"
*Adamant*
Return
Mirror Move
Brick Break
Flamethrower
Blaziken- adamant @ lum berry
-brick break
-rock slide
-earthquake
-overheat
Classic RS adamant blaziken...
Swampert - "Fin"
*Rash*
Surf
Rest
Take Down
Earthquake
Swampert- adamant @ leftovers
EV: Atk and HP
-Earthquake
-Return
-Mirror Coat
-Rest
Again, slightly limited due to lack of FRLG access... blah... no focus punching Swampert now... Feel free to take out return or mirror coat for Brick Break.
Crobat - "Goldy"
*Jolly*
Shadow Ball
Sludge Bomb
Wing Attack
Confuse Ray
Crobat- adamant @ lum berry?
-Shadowball
-Sludgebomb
-Aerial Ace
-Confuse Ray
Really... Crobat is highly limited without sub... blah! No toxicfusion with sub now...
Gardevoir - "Titania"
*Mild*
Reflect
Psychic
Thunderbolt
Future Sight
Gardevoir- modest @ lum berry/salac berry/chesto berry
-Will o Wisp/ chesto rest
-Thunderbolt
-Psychic
-Calm Mind
Calm Minding Gardevoir... it's always helpful to have a mini special sponge on your team
Aggron - "Tanker"
*Naughty*
Arial Ace
Metal Claw
Rock Tomb
Brick Break
Aggron- adamant @ leftovers
EV: Def/2 + HP/2 and Atk
-brick break
-rest
-earthquake
-double edge
Never use steel type attacks except Meteor Mash and rarely steel wing... steel attack sucks terribly... Once again hindered due to lack of FRLG but that's not your fault =/
The team isn't that bad at all actually. Just need to remember never use Take Down ever (never use that crap move). Also, look personality bonuses give you a 10% boost so use it to boost usually, one of your Pokemon's strongest stats.
Never use wing attack, as whatever wing attack can do, aerial ace does it better (and AA's PP isn't low too). Usually, don't use both special attack and physical attack on a Pokemon as that really hurts EVs. Finally, don't use 2 attacks of the same type on one Pokemon like mega drain with leaf blade together (both are grass type so just use leaf blade). This rule should always apply except for explosion.
However it's quite a good team. With a bit of further researches, you'll do just fine in battle.