I hate to say this, jen, but you'll need a hide like a rhino to live with a person like your mother in your life .....been there, done that, have the scars to show for it.
She knows what she's doing, nobody could be unaware of the hurt they cause ...just don't ask me to tell you why, I doubt the root cause is the same, but I do know my mother was not a happy woman, she didn't get the things she thought she deserved, and was quite happy to mess up anything around her.
My sister was like your brother in some ways, the golden child who did no wrong ......
Oh dear, I could go on but won't, i can only suggest you take a small step back now and again, concentrate on your family, they'll be there long after your mother and they are the important people in your life.
Don't try and talk to your mother .....you'll get nowhere ...you may have already tried
I'm sorry to be so long-winded, but know you're not alone, there are many of us who face the same negative attitude and utter **** from someone who should care about us .....take care and be strong xx