hi,
I think your mom suffered when she was a little kid, maybe her mom treated her the same way she is treating you right now and your brothers.
I think you should talk to her, it´s not fair what she´s doing, like a mom her job is to inspire you, motivate you and tell you how much she loves you. You don´t deserve to bre treated like that, obviously your´re not an indiot and you´re not ugly!!
So I think you should talk to her and if you don´t want to do that, then talk to a teacher, someone you truste but it has to be an adult so they can help you!! You have to tell them how you feel, do it for you and your brothers!
You´re not alone! You can do this!
Good Luck!!