The way I do hillwen with my party is:
Mage A (CC AOE DPS):
Icespear to 1
Increase Int Crit and MP
Mage B (DPS):
Hailstorm to 1
Max MP
Buy MP pots
Alchemists (Crowd Controllers):
Lifedrain to 5
Shock to 1
HP to 950
Gunslinger (Stray picker/Tank):
Rank Critical Hit to 5
WOTG to 1
400 HP
If done right you won't need shock till wave 3 (boss).
Place a barrier spike in the middle of the tunnel (try to do it as precise as possible).
This will causes the mobs to spawn in 2 groups.
The first 3 waves are incredibly easy since the Icespear using mage will use a 5 Charge icespear and this will instantly kill the mobspawn.
The Icespear mage should stand to the side of one of the 2 spawns then trow his/her icespear to the other side so both groups get caught.
Alchemists should focus on helping with just 1 charge of flameburst to keep them in place.
The Icespear will do enough damage.
The gunner should stay in the back catching any strays.
At wave 4 both Alchemists should have rank 1 Shock and should revolve to make sure Shock stays up 100% of the time.
At the end of wave 4 everyone must have at least 300 HP and 20 HP potions.(Mages need MP and Manashield)
This is because you WILL get hit by volatile zombies and you don't wanna screw up because you died.
At the end of wave 6 you will need to make sure you are able to use Shock 100% of the time check up on your Shock Crystals Mana Potions and Stam Pots.
If you don't have Shock up at all times you might fail this wave because Emerald Hyenas are a pain in the ass.
Make sure your Hailstorm Mage has Hailstorm up to use against the Hyenas
Once you see an hyena run by hit it with a 5 charge Hailstorm.
For Wave 8 you pretty much do the same as wave 7 except that the CC Mage should focus on icespearing Shriekers.
The best way to stop Shriekers is icespear even just 1 charge can make the diffrence now.
Questions can be asked.
Remember this is my way of doing Hillewen and I have succeeded almost all of the runs when people listend to me. (I don't get below the last wave anymore).
As for bosses:
One of the party members lures the boss.
Mage A and B get as close to each other as possible.
Mage A and B charge their Icespear and Hailstorm.
Alchemist A charges Shock
Alchemist B charges Lifedrain
When the Lich is in range of the Hailstorm mage attacks to make sure the spawns spawn.
The Ice spear mage freezes the spawn and the lich.
Alchemist A uses shock on the gunner while alchemy B uses Life Drain.
Gunner uses way of the gun and shoots the heck out of the Lich while also trying to defend the mages.
Alchemist A should change their weapon set to Fighter and use Charging-Strike>Somersault Kick.
Now Alchemist B should charge Shock and Alchemist A should use Lifedrain.
Repeating this untill the boss is death.