Well to me one thing is certain. There is no way that you are going to solve this problem from suggestions on this thread as sure as eggs are eggs, your brother is reading evey post on this thread and will always be one step ahead. He must be laughing his socks off. Indeed non of us know all the other posters here so he may even be one of them! Creepy!
BTW You haven't by chance got a Stik It note with your password stuck to the front of the screen have you?
One suggestion for you, how about when you finish a session putting the laptop in a locked drawer? Or is that a daft idea?