Re: brother and his irritating girlfriend
Usually when someone tries to 'solve' a problem by involving outside parties instead of the people directly involved, the intentions are not pure. Despite your claim that you don't care whether or not your brother marries this girl or has an arranged marriage, etc., it sounds to me like you're trying to influence the situation to put another black mark on this girl.
You're concerned about your little sister----so talk to her directly and in private and tell her you're concerned about her future and the development of her morals, etc. And perhaps separately have a respectful conversation with your brother and ask him to consider your little sister's impressionable state. Getting anyone else involved is totally unnecessary and is only going to serve your own need for drama or to 'stick it' to your brother's GF in some new, supposedly 'mature' way.