I would have a meeting with the residents and address the situation head on. I would tell them that it's obvious that they are not happy living in your community, and that being happy in their home environment is essential to a happy life. Suggest that since their lease is close to expiration, they start looking for an apartment home that better suits their needs, and you will work with them on a convenient vacate date.
If they say they do not want to move, then calmly explain how their behavior is a disturbance to your team and to their neighbors, and could be considered a violation of their lease agreement. Explain that you are happy to accept their complaints when they are realistic, but that the constant complaining about others without basis simply cannot continue, or they will be forcing you to ask them to leave. Do not renew the lease if you have a month to month option available, and let them know that you are offering them a "trial period" to see that they can improve their behavior. Hopefully, they will accept this attempt to work things out in a positive manner, and you and other residents will all breathe a sigh of relief. Good luck!