@Ritzii
Definitely keep Reuniclus and Conkeldurr on your team. You just need better movesets/natures/EVs etc. It might be hard for you to obtain these exact movesets, but I'll present them to you anyway:
Lapras @ Leftovers
Hydration
Careful
252 HP / 4 Def / 252 SpD
- Waterfall
- Curse
- Rest
- Ice Shard
That is currently the most popular Lapras set (and arguably the best Lapras set available). With Politoed's rain support, Lapras basically has "Full Restores" at its arsenal with Rest. Curse allows it to boost up its Defense and Attack, making it pretty impregnable and strong on the offensive at the same time. By then, Lapras can destroy teams with its STAB attacks: Waterfall and priority Ice Shard.
That doesn't necessarily mean your special attacking set is bad though. Something like this would probably be better:
Lapras @ Leftovers
Hydration / Water Absorb (you have Shell Armor which is cool to prevent hax, but it's just that the other abilities are more preferable)
Modest
40 Def / 252 SpA / 216 SpD
- Surf
- Ice Beam
- Thunder / Thunderbolt
- Rest
Sing is pretty unreliable, so it's swapped out for Rest for instant recovery. I'm sure you know what the other moves do.
The problem with the above sets is that you want to use Charizard. That alone will make your Lapras not as great as it can be since rain will lower Charizard's power and sun will lower Lapras's power. Removing Rest from Lapras's sets means that Lapras will not have much staying power and will die a bit too fast. I guess you can try out Thunder Wave on the slot and see how it goes.
For Charizard, yeah, get a new one. Mild is okay in that it raises its SpA, but it's not really that much of a good mixed attacker. The most common set Charizard uses is:
Charizard @ Choice Specs
Solar Power
Modest / Timid
4 Def / 252 SpA / 252 Spe
- Fire Blast / Flamethrower
- Air Slash
- Focus Blast
- SolarBeam
This depends if you're using Drought Ninetales or not. If not, remove Choice Specs and replace with Life Orb while also replacing Focus Blast with Sunny Day. This will drain Charizard's HP by 20% which is terrible, but it's not like it has much good options to use in this metagame. You also want a Rapid Spinner if you're using Charizard AND Lapras as both are Stealth Rock weak Pokemon and are prone to faint quickly if SR is set up. Anyway, moveset, Air Slash is a more powerful form of a Flying move that can flinch with good luck on its side (it's a special attack, which means you don't have to split attacking EVs). Focus Blast is mainly for Tyranitar, which can change the weather upon switching in and fully wall Charizard as a result. It's also for Heatran, which, again, fully walls Charizard. SolarBeam is Charizard's answer to bulky Water-types, which Charizard should be able to beat with sun support on. Moreover, SolarBeam helps against Rock-types that resist both Fire and Flying. Modest or Timid? Depends on you. Power over Speed thing.
My hands are hurting, so lemme type the sets of the others (not Serperior and Krookodile; I recommend you don't use them).
Reuniclus @ Leftovers / Life Orb
Magic Guard
Bold
252 HP / 252 Def / 4 SpA
- Calm Mind
- Recover
- Psychic / Psyshock
- Focus Blast
Or if you want to try a fully offensive one:
Reuniclus @ Life Orb
Magic Guard
Quiet
252 HP / 4 Def / 252 SpA
- Trick Room
- Psychic / Psyshock
- Shadow Ball
- Focus Blast
For Conkeldurr:
Conkeldurr @ Leftovers
Guts
Adamant
120 HP / 252 Atk / 136 SpD
- Bulk Up
- Drain Punch
- Mach Punch
- Stone Edge / Payback
For the last two slots, well, considering you have Lapras, Charizard, Conkeldurr, and Reuniclus, you have not only a Stealth Rock weakness, but the fact that Ghost and Dragon go through your team like a hot knife through butter. Get some Pokemon that resist one or two of them will do your team a good favor. Steel-types are ideal. I can recommend you either Scizor or Ferrothorn. Scizor is mostly for offensive stuff and Ferrothorn for defensive measures.
Ferrothorn @ Leftovers
Iron Barbs
Sassy
252 HP / 60 Def / 196 SpD
- Leech Seed
- Spikes
- Power Whip
- Gyro Ball
Ferrothorn also has a few other viable options you can consider. Thunder Wave is helpful to slow down threats and allow your other teammates to outspeed that Pokemon when switched in. Protect is helpful to regain additional health with Leech Seed and Leftovers (since Ferrothorn has no way to recover HP). It also helps stall the opponent out of HP if it's poisoned or burned.
The last Pokemon is up for grabs. With Ferrothorn, you have a good portion of threats covered. Remember Stealth Rock? Yeah, let's get rid of it with this slot:
Tentacruel @ Leftovers
Rain Dish (if you expect rain on your team, otherwise...) / Liquid Ooze
Calm
252 HP / 120 Def / 136 SpD
- Scald
- Sludge Bomb
- Rapid Spin
- Toxic Spikes
This gives you a useful Rapid Spinner and a burner/poisoner all in one. A problem you might have is that you'll be using two Water-types. Yeah, well, I'm not sure what other Rapid Spinners fit your team. Excadrill doesn't fit, Starmie repeats your special attacking Lapras, Forretress and Ferrothorn on the same team? maybe, and Donphan/Hitmontop are interesting options but I'm not sure how useful they're be for you.
Also, see
Blue Harvest's guide to EVs/IVs/Natures. You'll need it.
Well, good luck on your team!
