I'm not an absolutely top-class pokemon player, but I believe I'm qualified enough to answer this question.
Your team has some glaring issues.
Lapras:
Why do you want a Scope lens on a Lapras? If you want a Ice-Water type pokemon, use
Cloyster. It deals MASSIVE damage after a single Shell Smash, and with skill link as it's ability it's Icicle spear and Rock blast hits through Substitute, Focus sash, Sturdy, Multiscale and can wreck teams.
If you want more critical hits, use Kingdra with Sniper as it's ability holding a Scope lens. After using Focus energy, it has 100% chance of critical hits, and it's ability increases its power to 2.25 times rather than just 1.5 times.
Also, Ice beam is a special move. Never use special moves if you are running Adamant nature.
Diancie:
Don't use Iron defense and Calm mind. In most battles you can barely get 1-2 turns for setting up, and using both is impossible. By the time you've set up, you will be dead. Just use Calm mind, and drop Iron defense for Diamond Storm.
Dragonite:
Again, drop Hidden power. Dragonite is a physical attacker, and choice band powers up physical attacks. Hidden power is special. You might want to use Superpower over brick break, as you will want to hit as hard as you can and switch out when you have a choice item on. Similarly use Extremespeed over Aqua jet.
Heatran:
Heatran has a higher base special attack than attack. Put a modest nature on it, and replace ALL of your attacks with special ones. Lava plume, Earth power, Hidden power ice etc are recommended.
Chansey:
Oh dear god, an physically offensive Chansey....
Chansey has a base attack of 5. FIVE. And you want it to be a physical attacker?
And why did you even choose Chansey over Blissey if you don't use eviolite?
Use an Eviolite, drop all the attacks, put 252 EV's into both the Defences (252 on HP barely makes a difference when it's HP is already so damn high.), and use moves like Wish, Heal bell, toxic and Seismic toss.
If you want a pokemon to use those punching moves instead, consider Machamp or Conkeldurr.
Starmie:
This one is good enough. Not much to say.
I hope I helped, and that you will consider some of these points.
