I know you don’t mean to avoid the hurting coworker.  You didn’t intend to exclude the grieving mother from the group.  The bereaved widower is not left out intentionally. It just happens.  At the same time, you want to know that when you do step closer to someone in pain, you will say and do the right thing.  The skills most needed for compassionate comfort are to be Authentic and to remember to Ask questions for clarification and permission.