I hope the following information helps... .
I found the following on this website titled "Karpman Drama Triangles – Pathological Conflict -
https://bpdfamily.com/content/karpman-drama-triangle."
Before learning about this website (bpdfamily.com), I purchased "Stop Walking on Eggshells" by Paul Mason and Randi Kreger. There's information in the book on the topic of boundaries... .chapter 6 "Understanding Your Situation: Setting Boundaries, and Developing Skills."
Do you have a special friend that you can share what you have posted here? Someone neutral (not a relative nor spouse)... .who's willing to ask questions and provide constructive (not destructive) advice.
Is family counseling a possibility? If not, would you consider some individual counseling.
Yes, I understand your situation.
My BPD sister doesn't understand boundaries, and as an example, I decided to follow-up after a phone call with a letter which read in part... ."“As to the “when” we are together again as a family, any issues/concerns will be addressed by us, the parents. We have never made any requests from other family members to act on our behalf. Your role as Aunt and being part of our extended family is very important, to be supportive, encouraging and loving.” With that being stated, it’s important to us that you respect our wishes and not feel like you have to take any direct role to represent us... .in closing, I want to thank you for respecting our wishes."
The next time that I was in town, it resulted in a face-to-face confrontation in the parking lot of the apartment complex where my BPD sister lives at... .she expressed displeasure that I would even send such a letter, that she has never overstepped boundaries or something to the effect of "only one time"... .and that she was justified in doing so. My BPD sister stated that we are entitled to our own opinions... .went on-n-on about my major faults (meaning going back years). I simply replied that she does overstep boundaries and I ended the conversation with that I was sorry the way it turned out... .and my sister replied that she wasn't.
... .if anything, this was my first baby steps in making a change.