Do you have the quest from Maria to clear her name?
Are you sure you are at the right house? (the northern house just west of the healer's house)
Both doors (on the east and north sides of the house) should be unlocked until you expose Malcolm, at which point they are locked and require a key to open (which in turn requires Maria's recommendation to buy the house, after clearing her name).
AFAIK there shouldn't be a problem in the disk or download version with Pickpocket, if you have the necessary skill level for the NPC's level. Did you try a farmer, etc? The drunk Sweeny in the Ducal inn in Verdistis only requires level 1 Pickpocket (for the first test to join the thieves' guild), while the NPCs in the quarantine area require level 2). IIRC you need to right click on the ground to activate the skill, and then left click on the NPC.
Welcome to the forum.
