Hey nerd. The problem with your team is that it's too much passive. If I were to battle using this team, I would have probably become bored and stop laddering. Is this team even a Balance? No attackers at all; Sheer Cold Kyurem-W and Hex Lunala are not justified enough to count offensive.
Here are the problems this team faces:
Defensive Kyurem-W + Defensive Eternatus on same team
and 
are mostly for Kyogre. Having both specially defensive has no utility at all. Since both things cover the same threats, having both is redundant. The solution is to run Offensive Kyurem-W or Eternatus to keep both on same team.
You should opt out to make Kyurem-W offensive. Offensive Kyurem-W is an extremely underrated pick, but combined with a physical attacker this team can break anything pretty easily. Sheer Cold isn't just worth now imo, with other Kyurems and Lapras running loose on ladder, having Sheer Cold just baits out other Kyurem-W to wall you and absorb Sheer Cold. However, having Offensive Kyurem-W can give a huge surprise, as they get their Kyogre counter get out by surprise. So, without further ado replace that with this set:
Kyurem-White @ Life Orb
Ability: Turboblaze
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Roost
- Fusion Flare
- Ice Beam
With this set, you can lure opposing Kyurems into a death trap and surprise them with Draco Meteor. I prefer Ice Beam over Freeze Dry, so that you can do more damage to Yveltal (OHKO offensive sets). In case of Kyogre, it can't really touch you and we already have Eternatus so whatever. Life Orb with 252 SpA allows you to 2HKO NDM with Fusion Flare on the switch-in. Roost is pretty self-explanatory, it ensures your longevity.
Bad match-up against Marshadow
Marshadow is hell scary. It can come on anything like Kyurem-W, Lunala, NDM, and can force a switch-in. What's even scary is that, it can 2HKO / OHKO every member on this team with Life Orb / Choice Band. Here's the calculations to prove it:
252+ Atk Life Orb Marshadow Poltergeist (110 BP) vs. 252 HP / 252+ Def Prism Armor Necrozma-Dusk-Mane: 230-271 (57.7 - 68%) -- guaranteed 2HKO
252+ Atk Life Orb Marshadow Poltergeist (110 BP) vs. 252 HP / 0 Def Eternatus: 261-308 (53.9 - 63.6%) -- guaranteed 2HKO after Black Sludge recovery
252+ Atk Life Orb Marshadow Close Combat vs. 252 HP / 4 Def Yveltal: 285-335 (62.5 - 73.4%) -- guaranteed 2HKO
252+ Atk Life Orb Marshadow Poltergeist (110 BP) vs. 252 HP / 252+ Def Shadow Shield Lunala: 390-460 (81.5 - 96.2%) -- guaranteed 2HKO
252+ Atk Life Orb Marshadow Close Combat vs. 32 HP / 0 Def Kyurem-White: 595-702 (149.1 - 175.9%) -- guaranteed OHKO
So, what are you gonna do against Marshadow? All of your team is slower than it, and only Ditto outspeds it (can't switch-in though). There's one suggestion to it. An alternative spread for Eternatus that allows it to outspeed Adamant Marshadow while still staying SpD. Here's the improved set:
Eternatus @ Black Sludge
Ability: Pressure
EVs: 252 HP / 164 SpD / 92 Spe
Timid Nature
- Dragon Tail
- Flamethrower
- Toxic
- Recover
With the following spread, you hit up 350, which is faster than Adamant Marshadow at 349. Toxic is used so to fix the awful Ho-Oh matchup, also letting some space VS SpD Yveltal (Toxic Spikes gets walled by SpD Yveltal and any Ho-Oh set).
Two Defensive cores with Ditto be like: CRINGE
You ALREADY pretty much cover any offensive mon I can think of on paper, plus Lunala isn't really needed when we have Yveltal + NDM + Etern combo with Ditto. In case of Zekrom, it can be taken down by running Earthquake on NDM, plus Ditto can revenge kill boosted Zekrom. Same applies to Groudon here. So, why not instead fit a breaker that can form a synergy with Kyurem-W?
The best things that can come in mind are:
+ or 
God anyone will love this combo. KyuW Marsh can tear through balance like paper, so can QuickPass Calyrex-S with Kyurem-W. It is, indeed one of the most fantastic wallbreaking core. Here are some sets for it:
Marshadow @ Life Orb
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Poltergeist
- Close Combat
- Shadow Sneak
- Bulk Up
And
Calyrex-Shadow @ Focus Sash
Ability: As One (Spectrier)
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Nasty Plot
- Astral Barrage
- Psyshock
- Baton Pass
Here's one alternative you can try. Lunala can instead stay, and Ditto can be replaced with Marshadow. But all in all, that's your preference.
Tl;dr here's the updated team:
https://pokepast.es/412348e58277bb7a With Ditto
https://pokepast.es/76da2751dc03137a With Lunala
Hope this helps!
