Then, using weight maps to control the bones influence. Advice for adjusting bone strengths. The strength starts fading immediately after the minimum setting and is completely faded out by the maximum setting. So, it is important to not make the mimumim setting too low. But you'll need to experiment.
Areas like to torso require some special treatment.
Often, besides having the spine bones, you add a few extra bones extending from those spine bones and out to the stomach area, to add more influence around the stomach to keep it from being pulled by other bones. Actually, it's more of an L-shaped extension. This second bone should point either upwared or downward. So together, your two child bones for an L, with the second child bone being parallel the the spine. And the second child bone is just on the inside of the stomach.