the only way to make him stop is to have a man to man conversation with your brothers about what would happen if he were caught by police in white ass europe. I'm not sure what the laws on weed are in your country but do the research and let him know. it needs to be his choice to stop otherwise hell continue to get high in secret like most teenagers. you are a good older brother though, although i don't recommend physical abuse.I got his dealers number
also btw, certain dealers lace their weed to get the user addicted enough to come back. he should be careful. especially if the dealer is someone he doesn't know. cadaans are usually the type to do that fucked up shit. regular weed doesn't make you addicted, so if he feels withdrawals there was something else in what he smoked.