Jenny, I second (or 4th or 5th) the motion not to tell them ahead of time. They have shown you no courtesy, so there is no reason to show them any. Cancel the lease and on the day you are going to move out have your friends show up and help you pack -- stick it all on a rental truck and LEAVE. And as the truck is leaving, mention to them that the lease expires in 3 days and they had better find another place to live. If the utilities are in your name cancel them, too, for the Day After. If you've got a cell phone, cancel the telephone service.

If you can pick a day or time when as few as possible of them will be home, so much the better. Bullies like to run in packs, and if they aren't all there is may temper their behavior. If that's not possible, I advocate an early start (like 7am) so everything gets packed up and nothing gets left behind, because you aren't going to want to go back for any reason.

There is absolutely NO reason to risk yourself, your property or your mental health doing anything for these moochers!