1/ what is the strong role of each class (i.e cai lin very good at early game, can farm stuff for other guy, centau guy is good at regen hp and tanker)?

2/ using centau guy, have kolloon set, weapon forged (2), demon king mirror + flame & frost talisman, but i still cant defeat flame + frost demon king to do quest ( for 2 key treasure), what i should to do?

3/ how to get 2 extra class, i see only 5 class to choose?

4/ sorry for my bad engrisk!