Well if you can get them to admit the took your stuff you that to blackmail them to get your stuff back. Just say you have in on a text that they said they took it and say you will call police. Call apple a cancel the watch and say it was stolen I believe they can kill the watch making it useless. As for fighting them I am sure your teacher has told you that you can only use your karate in self defense and that if you use it to harm someone you can be charged with assault or even attempted murder. You are a trained killer ( I mean that lightly) but you know what I am talking about. What goes around comes around.

Are their cameras in the halls or anywhere around where you live maybe you can ask security to look at the video and see if you can see anything.

Did you know these guys were like this if so why did you invite them over or at least hide your stuff in your room.

Young man threaten them that you are going to the police and will tell all there names if you don't get them back .

guys some one tell me