I'm mostly just going to visualize what 'Slash said for you, so don't give me best answer. A lot of this isn't my work.
Smeragle @ Focus Sash
Ability: Own Tempo
EVs: 252 Spd / 128 Def / 128 SDef
- Sticky Web
- Stealth Rock
An extremely versatile lead. Nice Smeargle set. I put the ability Own Tempo because, frankly, it's the most useful ability Smeargle has access to.
I personally would switch Darmanitan for Infernape, but that's your call.
Infernape @ Life Orb
Ability: Iron Fist
EVs: 252 Atk / 252 Spd / 4 HP
- Flare Blitz
- Ice Punch
- Close Combat
- Slack Off
Flare Blitz because it's still more powerful than Iron Fist Fire Punch. Ice Punch for Ground, Rock, and Flying coverage. Close Combat for Fighting STAB. Slack Off to heal recoil damage if you anticipate a switch (I run Slack Off and it actually works out usually).
Let's keep Latios and scrap Dragonite, because you a have to set Dragonite up while Latios can just wreck with a specs set.
Latios @ Choice Specs
EVs: 252 Spd / 252 SAtk / 4 HP
- Shadow Ball
- Draco Meteor
Run specs over Life Orb because there's a higher power boost and you don't get recoil. Draco Meteor with specs is extremely powerful and will 1HKO basically anything that's not specially defensive. Shadow Ball kills Psychics and Ghosts, and Defog is to clear hazards since Smeargle doesn't run Rapid Spin.
In place of Dragonite, let's get a physical tank that covers Fairies, like 'Slash said.
Aggron @ Aggronite
EVs: 252 HP / 252 Atk / 4 SDef
- Heavy Slam/Iron Head
- Stone Edge/Rock Slide
Boost Attack and Defense with Curse and get great coverage with a Ground-Fighting core. Choose Heavy Slam or Iron Head based on your confidence in Aggron's weight versus a flinching chance (I recommend Heavy Slam). Choose Stone Edge or Rock Slide based on power versus accuracy.
You've got Sableye here. I think you could use another sweeper, but it's good to have a taunter and burner. It's also good because you have a bit of a Fighting weakness, and he counters Fighting-types extremely well. He also blocks Rapid Spinning.
Sableye @ Leftovers
EVs: 252 SDef / 252 HP / 4 Def
- Night Shade
This is a good Sableye set. I actually run pretty much the same thing. I set the ability Prankster and a Calm Nature.
Next, in place of Chansey, the Florges set 'Slash recommended.
Florges (F) @ Leftovers
Ability: Flower Veil
EVs: 252 HP / 152 Def / 104 SDef
Flower Veil means Sableye can't taunt it, which is really nice. Wish can help itself or another teammate who can't heal themself, particularly your physical tank, Mega Aggron. Aromatherapy means status conditions won't be a problem for your team, and Toxic cuts other annoying walls' HP. Moonblast is there for its attacking move. Nice set, 'Slash!
I hope this helps you out. Poke'slash made some really good suggestions, and I also made a few tweaks.