1. How do I unlock doors? I'm not kidding, I can unlock chests but when I choose open lock and click on a door my rogue approaches the door but all that happens is a "Door is locked" floating text. 2. Can I switch weapons in any other way than via inventory? My Ranger and Thief use bows but when enemies get too close or my fighter dies I want them to switch to a melee weapon. However when I do it via inventory I can't attack in the same turn. 3. Not really that important but I installed Co8 2.0 mod with all options and I still can't enter the brothel in Nulb. 4. Are there some requirements needed for Mona to give me her quest? All she says is "I see no way in which you could help me". My party is of good alignment if that matters.
Hmmm... you could always try a few times and see if that helps. It could be that your skill level is too low to beat the DC of the doorlock. Other than that, may I suggest that you try using the Knock spell? I believe it has flewn through my ears that some doors can only be opened by that spell. Other than that, I don't have anything useful to add :/
1. Select thief. Mouse over the door til you get the padlock icon. Right click on icon. Select open lock from radial. He should give it his best. Or knock spell. 2. It's supposed to be that way. It takes time to switch weapons. The only way to change that is the Quickdraw feat. 3. Ask the gyspsy about it and tell her you want to go in and look at the pictures. You will appear inside. That was the best Co8 could do. When you leave, your last character will be stuck in the wall. Don't worry. Just go to the nearest real door and go through with another characther. You'll all appear inside the real building. 4. Are you talking to her with your diplomatic character? Have you tried other conversation paths? Otherwise, dunno.