MONO FAIRY (HELP)

In a group, I'm the Fairy type Gym Leader.

I always seem to lose though. I have M-Alt as my Mega.

Help?

Mallow (Altaria) (F) @ Altarianite
Ability: Cloud Nine
Shiny: Yes
EVs: 156 HP / 248 Def / 104 SpD
Bold Nature
- Hyper Voice
- Flamethrower
- Roost
- Heal Bell

Kamikaze (Azumarill) (F) @ Sitrus Berry
Ability: Huge Power
Shiny: Yes
EVs: 248 HP / 252 Atk / 8 Def
Adamant Nature
- Belly Drum
- Aqua Jet
- Play Rough
- Ice Punch

Bella (Aromatisse) (F) @ Leftovers
Ability: Aroma Veil
Shiny: Yes
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
IVs: 0 Spe
- Toxic
- Trick Room
- Protect
- Moonblast

Basil (Granbull) (M) @ Expert Belt
Ability: Rattled
Shiny: Yes
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Crunch
- Fire Punch
- Earthquake
- Play Rough

Carissa (Clefable) (F) @ Life Orb
Ability: Magic Guard
Shiny: Yes
EVs: 248 HP / 156 Def / 96 SpD
Calm Nature
- Stealth Rock
- Fire Blast
- Moonblast
- Wish

Also looking for a sixth Pokémon

(Mega) Altaria doesn't count for mono-Fairy teams because it's not a Fairy to start with. The rules for monotype teams state that all Pokemon have to share a common original type in their base form, no Mega Evolutions counted. Mega Gardevoir is a replacement:
-Psyshock
-Hyper Voice
-Focus Blast
-Taunt/Will-o-Wisp/Calm Mind
Nature: Timid/Modest
EVs: 24 Def/232 SAtk/252 Spe
Item: Gardevoirite
Ability: Trace

Ice Punch is useless on Azumarill because Dragons are already hit hard by Play Rough. Play Rough still OHKOs Dragonite after Multiscale is broken:

252+ Atk Huge Power Azumarill Play Rough vs. 0 HP / 4 Def Dragonite: 372-440 (115.1 - 136.2%) -- guaranteed OHKO

The preferred coverage move on Azumarill is Knock Off to remove non-Mega Stone items. Azumarill also runs significant Speed investment (164 Speed EVs) to outspeed 0 Speed Skarmory.

IMO, Whimsicott or Klefki are better support Pokemon than Aromatisse, as the former has Prankster to give its status moves priority and the latter doesn't share any weaknesses with any of the other Fairies you have:
-Moonblast
-U-turn
-Encore
-Stun Spore
Nature: Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Prankster

Klefki:
-Spikes
-Play Rough/Foul Play
-Thunder Wave
-Magnet Rise/Toxic
Nature: Careful/Calm
EVs: 252 HP/4 Def/252 SDef
Item: Leftovers/Sitrus Berry
Ability: Prankster

Sylveon is a better hard-hitter than Granbull, IMO, as Pixilated Hyper Voices are ridiculously strong:
-Hyper Voice
-Psyshock
-Hidden Power (Fire/Ground)
-Baton Pass
Nature: Modest
EVs: 240 HP/252 SAtk/16 Spe
Item: Choice Specs
Ability: Pixilate

or
-Calm Mind
-Hyper Voice
-Substitute/Wish
-Baton Pass
Nature: Bold
EVs: 252 HP/240 Def/16 Spe
Item: Leftovers
Ability: Pixilate

Clefable is missing some EVs. 252 HP/172 Def/84 SDef allows Clefable to avoid the following 2HKOs:
-Jolly Mega Lopunny's Return
-Latios' Psyshock,
-Jolly Mega Gyarados' Waterfall
-Mild Life Orb Black Kyurem's Ice Beam

Leftovers is a better item on it for passive recovery. Also, Moonlight or Soft-Boiled is highly recommended as more reliable recovery for Clefable itself.