These travel in groups of 3. The lead(also known as "the mother") always drops a NQ organ. I have found, but cannot confirm why, that if you pull the last one you can sometimes pull the lead without having the 2nd one agro. Its hit or miss, but it works sometimes. - Drayco Hades
Om'xzomit are actually found solo or in groups of two. Regardless, if your going after organs you'd be better off killing the lower level Ul trios. Even with the extra mob, they're much easier to solo and the singles seem to have a terrible drop rate on organs.