I'm glad you decided to move out. I don't know how to advise you to approach this, though... Maybe talk with your brother first, see if you can get him to understand? Then he can help you talk to your mom about it. Otherwise you'd have to hope you can get her to understand that you need to go be an adult.

Frankly it's extremely selfish of them to put you in that position. If they love you they should want you to be happy. =/ I hope everything works out.