I didn't see anyone else address this but are you fully aware of what substances that they may be ingesting as part of their body building. Obviously things like steroids can result in increased agression. Even so called "natural supplements" can have detrimental affects and some are laced with steroid like chemicals that may produce the same effects along with increases in testosterone levels.
However, it sounds like your sons aren't necessarilly being the agressor but rather just stepping into situations in order to help out others or perhaps not backing away from confrontations. These issues have nothing to do with body building per se but it might tangentially contribute to a feeling of overconfidence and perhaps a penchant for "taking on situations" without much consideration since intense body building requires attacking the weights and "psyching oneself up" and this kind of mindset can bleed into other areas of life - not always bad.
The thing you need to stress with your sons is learning when there is a time to stand up and not back down, to be agressive or handle a situation, to come to the aid of others, and when one should walk away or extract themselves from a situation even if it means seeming cowardly or losing face. One thing that you need to teach them is that even a strong muscle makes little resistance to a sharp knife and no matter how buff they are they can lose their life at the end of a gun. Thus the whole bar-fighting thing needs to be cut out and avoided unless their own lives are in danger or they can "safely" intervene. Most bars have bouncers and persons PAID to break up fights so they should not be doing that unless it is like their friend or something and only to the extent to stop the violence not add to it.