Although it initially sounds like the real problems in this situation are your two co-workers, the actual problems are your supervisor and manager. You and your co-workers have advised them of a serious situation, and these leaders have taken no meaningful action.
When management allows employees to act like bullies, it indicates that management is rather clueless in understanding the importance of listening to the staff and treating all employees with respect and trust. On a broader basis, one has to wonder about the way in which the company itself is being managed. After all, if management is not bothered by employees who abuse their co-workers, it is hard to know if anything is bothersome to such leaders.
At this point, you should meet again with your supervisor and manager, describe the specific behaviors of your difficult co-workers, spell out the problems that their antics are causing, and ask these leaders for help. If these leaders continue to be helpless, you should seriously consider either going over their heads or going over to another organization.
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