shaman farts and then can't do anything for a while. He heals the others, so doing a little damage to them can be a strategy to distract it, but he will undo anything short of death on the others.
that means your best bet is to play in & out with the shaman to get him to do the toxic gas attack and then once that is done he can't do it again for a while so you rush him and kill him. Then mop up the others.

if you get a brute/shaman pair, the shaman is still the focus but you may want to simply run away. Its perfectly fine to run away from stuff you can't handle.

-> anything unaware of you takes a lot more damage from that first bow hit from stealth.
-> honey is really nice to heal up any damage you take in combat at the low levels.
-> shaman will ninja you even at high levels. That one time you forgot to eat and pay attention, bam, death by toxic gas. They are the most dangerous thing in the forest because they will blindside you without as much warning.