I actually managed to do the twisted tree battle with one man down before I learned about target priorities. My approach was:
1) Leave Astarian at home because that entire area is running water
2) Two melee characters + SH + Gale
3) SH and Gale get jump cast before the fight starts, one of melee guys gets it as well
4) SH and Gale jump on that small column where nobody can reach them. The only possible attack becoming spitting from below at a disadvantage because of height.
5) melee characters jump around and kill things
6) Use fire cantrip on tree things and also on those branches that can entangle you. They both burn good
Everything in shattered sanctum you can cheese up by moving to the upper level and sniping from above. Sometimes it is even 1 shot when they can't see you.
