problem with latest thieves guild quest

[purplehead]

so, I am about to finish thieves guild. I stole the elder scroll from imperial palace's library. that was the easy part. but i cant get out. i pass the moth priests sneaking, but when i go to this room with battle mages they ALWAYS find a way to notice me. I tried invisibility, they saw me. I tried tcl cheat but appereantly im supposed to get into that room and one or two mages never leave. after trying 5 - 6 times i decided to fight them since i wont be banned from thieves guild for killing people. but when i kill the mages i get banned from mages guild. so I gave up, used the movetoqt cheat for another quest and got out of the palace. I tried to find gray fox but he's nowhere. I have to go back and go through these doors and stuff. So i got in again, and it shows that i need to get into the imperial guards living quarters and it requires a key, i tried getting a key from one of the guards a few times but none of them had it! what should I do?