Twilight's Eve Final , Imp (all) Problems

Anyone who play this map? I'm playing with my friends and we still cant kill boss from imp 1 to 4. We have priest , druid and grand templar but priest and templar die with 1 or 2 hits(lv 260 , 280 , 290 all 4th stage). Bosses do a spell(green circle ) and one shoot anyone or stun and istant kill healer or dpser...Could someone explain me something? Only druid need defence(bear form ) or all ? How can dpser and healers survive? What's best equip to defeat imp dungeon?
For example , Boss of Impossible 1(that one after grimworld , make a spell that almost istant kill druid(about 3000 defence and 26k hp)
Thanks

I would be happy to do some imp runs with u. I can get 2 friends with me so wer are 6 in total, maybe even 7. tell me when it is possible that u and ur friends get some time to play.