All of your ideas are terrible. STOP.
This is not a situation you can fix with rules or flexing your 'boss muscles'. By trying to 'assert your authority and end the talking' you are just digging a very deep hole for yourself.
You need to address this issue on an individual level by talking directly to the employees or employee in question.
Why are they saying that the pay is not fair? Is there anything you can do to fix it? Is your pay fair according to market standards? If so, give them links.
Is it not fair? Then reveal the arrangements you made. Tell them why you paid someone what you did.
In the end, you need to tell them they are paid what they are paid for X reason- and if X reason is not good enough, they are free to go. And if they are there temporarily until something better comes along, that you understand and would appreciate a warning if they do decide to leave.
If you're being reasonable on this, it should be fine. On the other hand, you might have someone who is a troublemaker, and it might be best for you to just get rid of this person. Someone who is a rumor monger/bully might be causing other problems in your business as well.