Clearing Chapter 2 of the Campaign on Normal is not very difficult if you follow several important steps. 

The element of the enemies in the chapter is wind, so take 1-2 of your Earth invokers that you have in collection and even if they are common or uncommon level them up to level 20+. 

Do not forget to equip relics on every Invoker in your team in the Invokers menu.

If you have 3 or 5 reclis from 1 set (Attack or HP) you will get a 15%-45% bonus to attack or HP so make sure every invoker on your team is equip with relics.

You can use Auto-Equip at this stage. 

Chapter 2 - Normal - Example Team

Video Guides - All chests locations

Here's a playlist with video guides where to find all chests on all levels to get 2nd star in each level. 

Invokers: Titan Legacy - Campaign - Normal - Chapter 2 - All Chest Locations