How do I defeat Thunder and Bolt? I'm three levels higher than them and still lose every time.

stormy
1.equip with Myrmidon gear(it can be found in the trade broker and make sure its around the same level as the pet )
2.make sure you put stormy in the second party slot

shadow:
1.equip with assassin gear (again it can be found in the trade broker and make sure its around the same level as the pet)
2.put shadow in the front(first party slot)
3.you should add health on shadow instead of strength

other tips:
1.unlock the third party slot
2.buy potions and revives
3.keep leveling up your pets

also make sure you get rare,mythical or legendary gear

They can't unlock the third slot until they reach Umbra Forest, and unless they buy it, they can't get mythical gear until they've completed the Viridian Meadows and unlocked the Nightfall Bandit Dungeon.

Shadow absolutely doesn't want Assassin gear- that's for Water/Earth tanks, not Shadow tanks. Shadow tanks want Illusionist gear.

Try to get some Rare or Epic Myrmidons for Stormy (Rarity of equips can make a lot of difference stat-wise) and fill out Shadow's equipment with Illusionist where possible and Evoker failing that.

Once you can, I'd suggest trying to get your hands on legendary-rarity equips, but for the moment rare/epic should be okay.

Thanks!