They do need to know that have to respct you, you are the boss in your house. it doesnt get any easier. think of it like this they are testing the waters and also getting you preperred for the time they leave. if they never do anything wrong you would never want them to move out
even when theymove out the drama never stops. i raised my kids knowing great values and all you can do i keep inforcing htem and hope they come around sooner then later