Welcome kitty1: I'm sorry to hear you are having problems with your mother and brother. Have they both been diagnosed with BPD? Are either of them getting any treatment?
They are very codependent and I feel he treats me like the enemy so they are closer and it works for her.
In what way are they codependent?
I am burdened with all the responsibility and guilt when thinks mess up for them both? How can I learn to stop contributing to this cycle?
Can you give an example of a recent situation?
This is a safe place to share. If you are able to share some examples, we can better point you to some specific lessons. In the meantime, you might want to browse around and click on some links to workshops and information. There is a "Lessons" thread tacked to the top of this message board and there is a large green band at the top of this page, with a "Tools" menu. These are good areas to find helpful information.
I look forward to hearing more of your story.