Working skills in the house - 3 accounts. 1 owns the house, 1 co-owns, 1 no-friend (i.e. grey). I could perform random stealing on the grey, though not the blue (stealing skill <80, not in thief guild). Could not repeat on the blue.
You can steal from gray and red without reference to the guild, I just read about it and did not try it myself. I always belong to the thieves guild. But the information about the blues is accurate. I think this was done so that detectives would work and not be useless.