Challenge.
Classic straw man. Your earlier point up-thread was that he was an intruder and therefore could be shot. Now you are saying "I have no legal say in the matter." Appleas and oranges. You can, of course, tell the teenage friends to leave. If they refuse, you can call the cops. If they threaten you, you can defend yourself. However, you can't block their exit and then shoot them as intruders.
Nice try with the strawman, though.
If I make it abundantly clear to someone in my home that they are not welcome in my home and their response is to kick me, they are indeed an intruder and they will be subject to any self-defense measures I undertake.