I'm running the carrion crown AP for 3 people right now. The party consists of a barbarian, a ninja who took a couple levels of cleric for in game flavor purposes, and a witch. They're just about to end the second book and have been doing just fine. It's a little tough at times, but they haven't had a single death. I've always been in the mind set of "if you play smart you can overcome most anything" and these 3 players reassure me of that in how well they overcome the odds.
