Welcome
Shilohgrace!

I'm glad you found us and took the first step to post a bit of your story here.

We're an online family who really gets what you're going through, and you'll find lots of support and listening ears here. This is a safe place to share.
Tough stuff. No other words to say about the craziness that you're caught up in when you have a pwBPD (person with BPD) in your life. My mom was an uBPD, and because I lived far away from her when I was married and had kids, she didn't try to triangulate them like they so often do. She definitely began to try and triangulate my sister's children though, because she helped to babysit them. When my mom and my dad divorced, there was lots of triangulation to try and get us to side with her.
Triangulation is a part of all of our lives, but the triangulation that takes place in a relationship with a BPD steps it up to a much more serious level. One suggestion I would share is that you not leave your children with her alone at any time. You are their protector, and while you may not fully understand all that there is to know yet about BPD, as a child of one, trust me that it's important for both your sake and theirs. You don't have to feel badly about the boundary either. There's no shame in being protective.
There's a saying we have here: you don't need to JADE (justify, argue, defend, or explain). That goes for any interaction with your MIL or DH (dear husband) if any questions arise about you staying with the kids if they're with her, or any interaction that may come about. You keep interaction BIFF (brief, informative, factual, and friendly), and you can walk away.
I feel like she has affected my life in such a negative way that she has me questioning my own self worth and made me feel like I've caused our family all its problems.
Ah, this is SO classic with a pwBPD. I grew up feeling as if I had done something wrong, all the time. Please know this for sure: you
are not the problem. Ever. This is how they control and project in order to get what they want. She will not change so you need to do the protecting of you and practice self care and kindness. Have you ever read the book
Stop Caretaking the Borderline or Narcissist? It's excellent, and I highly recommend it! It has been so helpful to me and to others here as well.
I know others will chime in soon. What do you think about those suggestions? Looking forward to hearing more of your story. Hang in there.
Once again, welcome!

Wools