I finished the game once with a chaotic good sorcerer, so I hadn't the need of Edwin in my party. I'm now restarting it with a neutral bad berserker (Celestial Fury forever ) but well, I can't imagine being doomed to use Jan Jansen as my ONLY mage in the party... So the point is, when I had my sorcerer, I worked with the Thieves and now that I am evil and since I'm restarting it, I try the other way... but, I didn't even asked for a single quest for the Shadow Thieves, so I didn't get my pass to Maevar's guild. Is there another way to get in so I can get Edwin ?

Well, you could always go up and knock on the door. If no one answers try to pick the lock and cut your way into the Guildhall to talk to him. I don't remember when I spoke with him, but I didn't do any of the quests for the thief guild either.

BK

This can't be done, the doors need to be opened from inside the guildhall, or by some Thief key, though I doubt I'll ever be able to get in again... The access to the guildhall is granted by Gorch, and he has no key

If you're no averse to a little cheating then you can use Explore Area to remove the black patch behind the doors and then Ctrl + J to jump into the Guildhall

Edwin won't be in the guildhall until you have done the first quest fot Mae'var. Should just try and see if Renal will give you the quest.