ok so i went into the lich mad wizard all my party lvl 12 and he takes me easily in "easy-mode" any suggestions ? 

I was able to get him using the same method I got the rest of the apprentices. My party is Rogue Watcher, Eder, Aloth, Grieving Mother, Hiravias, and Durance. I lined up the Rogue, Grieving Mother, and Hiravias at the doorway, with Aloth and Durance behind them. I walked Eder forward to initaite the conversation, then once combat started, I ran him back to the doorway, while Aloth started casting Fireball and Hirvius Plague of Insects at maximum range. Then I stopped Eder a little ways away, but still within distance that Durance could clip him with heal spells. Everyone at the door used ranged weapons and summoning trinkets (wurm, shades, and beetle). Grieving Mother would cast Mind Plague on some of his minions so charm would spread through them. Hiravias would help out with healing Edir by using Winter Wind and Cleansing Wind, simultaneously keeping him in good shape and clearing out excess minions. Oh, also, my watcher had Necklace of Fireballs, so she would join in on Aloth repeatedly fireballing the group.

 

This set up last roughly half the fight until Eder went down, by that time only one or two of the lich's minions were alive, one attacking the other thanks to Grieving Mother. I stupidly ran out of level 5 spells with Durance so I couldn't raise Eder, but I ended up just surrounding the lich and beating him down. I believe I switched to Minolette's spells once my party started mixing it up, so I wouldn't catch my own group in Aloth's AOEs. 

Bottlenecking didn't help me. They AOE'd the hell out of my party. Divide and conquer worked.

I cant seem to get into the room I killed everyone and i still cant pass the door, can someone help?

Ok, it's maybe stupid, but how do I end this sub quest? I killed the mage - I killed everyone in there - and the quest didn't end. Something I need to pick up in Cragholtd? Where is it?

I think I have it figured. You actually need to look at the notes you collect. Once you have viewed them an additional dialogue option should become available

Bottlenecking worked perfectly for me. Just make sure everyone you send to the frontline has high defenses, while everyone in back rains down damage. It also helps to put a trap at the archway. Summon a few creatures while you're getting into place, and a few more across the fight (I recommend against summoning them all at once, otherwise they'll die fairly quick to AoE).