the girl said her brother would be cool with you guys smoking. he wasn't. we can conclude one of two things: either the girl is an idiot and doesn't understand her brother at all, or the brother would normally have been cool with it, but wasn't for some reason in this case. if the girl is an idiot you should be mad at her, not the brother or parents, for getting you in trouble. if the brother would normally be okay with it but wasn't this time chances are it's because he doesn't like watching guys put moves on his sister and he isn't going to be scared of getting you in trouble again if you try and retaliate. and, honestly, you aren't in much of a position to do anything without threatening him, in which case he can easily tattle again and the parents will just like you less than they do now and only be more convinced you are just a stupid stoner who isn't good enough for their daughter. forget about the money, or start dealing to make it back
sparknotes: you won't be able to get back at brother cause he'll just tell on you again, best option is to either forget about it or sell drugs to make the money back.