You chose to protect yourself. Kudos for you. Since pwBPD resist boundaries, that was you properly setting and implementing a Boundary
in response to poor behavior, one of the
Tools and Skills we advocate here.
Also, that your other sister was "convinced" to cast you as the evil enemy is probably also due to the repeated pressuring and perhaps intimidation.
Years ago we had a father here with a young daughter whose ex was evidently Histrionic and what he experienced was horrendous.