Re: Wrong girl for brother
Maybe you should try to talk to your brother again before going to your mother, and explain to him how you feel you've been placed in an impossible position where you want to be able to retain the trust of and stay honest with both him and your mother? Ask him to come up with a solution himself? Listen to him first, and try not to moralize -not saying that you are- while explaining you point of view.
And by the way, I'll advise against unnecessarily involving other people or writing letter anonymously to your mother.