I'm not an expert at NU, per se, but I can make changes to individual Pokémon. Changes will be in bold.
Seismitoad@ Life Orb
Ability: Water Absorb
EVs: 252 Atk / 48 SDef / 208 HP
Brave Nature
- Earthquake
- Drain Punch
- Power-Up Punch
- Scald
Life Orb helps 'Toad nab some more KOs. EVs have been redistributed to accomidate more bulk on both fronts. Adamant was changed to Brave so that Scald is doing as much damage as possible. Surf was replaced with Scald for the chance to burn.
Mesprit@ Focus Sash
Ability: Levitate
EVs: 252 SpA / 252 Spe / 4 HP
Timid Nature
- Psychic
- Healing Wish
- Thunder
- Stealth Rock
Timid Nature for more Speed, as base 80 isn't the greatest. You have no Rocks setter, and with Focus Sash Mesprit is almost garunteed to be able to set them.
Uxie@ Leftovers/Damp Rock
Ability: Levitate
EVs: 252 HP / 252 Def / 4 Spe
Impish Nature
- Heal Bell
- U-Turn
- Rain Dance
- Memento
I changed Uxie to a more defensive variant who can help support your team by setting Rain. Leftovers can be used for recovery while Damp Rock lengthens the Rain. Impish Nature for more Defence. U-Turn is to escape so that you can come back once the raij ends. Memento is a nasty surprise for opposing sweepers. Rain Dance boosts Seismitoad's Scald, makes Mesprit's Thunder perfectly accurate and nullifies Steelix's Fire weakness.
Audino@ Audinite
Ability: Regenerator > Healer
EVs: 252 HP / 252 Def / 4 SDef
Bold Nature
- Wish
- Protect
- Calm Mind
- Dazzling Gleam
Try to refrain from Mega Evolving until you really have to, as Regenerator is infinitely better than Healer. EVs and nature changed to be more bulky. Calm Mind is a better setup move than Charge Beam because of the Sp. Defence boost. Dazzling Gleam is a more reliable STAB than Draining Kiss.
Steelix@ Life Orb
Ability: Sheer Force
EVs: 252 Atk / 252 SDef / 4 HP
Brave Nature
- Gyro Ball
- Earthquake
- Toxic
- Crunch/Heavy Slam
Life Orb is generally the #1 item for Sheer Force users, and Steelix is already slow as heck. Brave Nature powers up Gyro Ball. Toxic allows Steelix to cripple walls like Audino. Crunch provides Ghost and Psychic coverage, while Heavy Slam is a reliable secondary STAB attack.
Electivire@ Expert Belt/Choice Scarf
Ability: Motor Drive
EVs: 252 Atk / 252 Spe / 4 HP
Jolly Nature
IVs: 31 Atk
- Wild Charge
- Low Kick
- Ice Punch
- Earthquake
Expert Belt buffs supereffective hits, and Electivire has excellent coverage. Choice Scarf lets it outrun an KO threats it would be unable to deal with otherwise. Why 30 IVs in Attack? You need all of them. Low Kick is your only Fighting attack (seriously, three?). Ice Punch covers pesky Dragons and Earthquake is Earthquake.
I hope this helped you!