yeah i agree, maybe get your dad in it too. But dont act like youre ganging up on her, just tell her how you both feel. Your mum needs to learn to let her 'little boy' go, otherwise its bad for him coz he wont learn anything about the real world and will always rely on your mum.
Also, it might be worth having a chat with your brother? Tell him he needs to grow up, explain how awesome uni was for you, and you're really glad with how you did it, as you've learnt so much about life etc