a) and b) If they're not holding it, you can use Thievery. Currently, two of them are armed with quarterstaves, and the other two are holding torches, but they all have swords and knives on them. If you succeed in taking it from them, or fail by a small margin, they wouldn't notice that you have taken the item, though you have nowhere to hide it, so you'd have to hold on to it, and they would notice that.

c) Generally, I'd say yes, though it can vary by circumstance.