You need to show them who is in charge, because it sounds like they think collectively they are.
Consequences for disrespectful actions. No negotiating. Once they get you are the boss and the boss expects certain behaviours they will be much better behaved. Don't ask for good behaviour, tell them. The mocking would be responded to with chores and then sitting on a chair for the remainder of the day.
I am going to sound old but...........wow, to mock an adult wouldn't even enter our minds. If ever did that I would have been grounded forever and not have been able to sit down for a long while.