Hi Riazebmom,
Welcome to the BPD Family
It's great that you decided to jump in and join us, this is a great place to get support, tools, ideas, strategies, and sometimes just a place to vent. We all have someone in our lives with BPD/BPD Traits... .we "get it".
Can you tell us a little more about your situation? Do you all live together? Separately? Is your dad in the picture? What is his role? What kinds of behaviors are you experiencing regarding your mom and your sister? Is anyone receiving therapy?... .okay that's it for the questions

Just trying to get a feel for your situation.
I'd also like to point out the box to the right --> everything there is a link to more information. You might want to check out the material in the "Lessons" section when you have the time.
I hope to hear more of your story.
Panda39