How "little" is your little brother? Because that's starting to sound less like just being a newbie and making newbie mistakes, and more like a much deeper personal problem.
Here's how I would handle him. Bring the book(s). Make him write down his lists, with point costs and FoC labelled clearly. If he tries to do anything at all, even if you know it's legit, make him look up whether or not he can in the book.
Basically, force him into honesty, and more importantly make sure he knows that people won't put up with bullshit. Letting him get away with things now will make him think he can get away with things later--things that might be far more serious than cheating at a friendly miniatures game.
And if your parents complain, explain why you're treating him like that. If they can't appreciate a little harmless but necessary discipline, then the problem might not be with the kid....