Thank you for these thoughtful responses. They are thought-provoking for me.
I should clarify that I'm the mother here -- no wife involved, only a husband who also gets blamed for a lot but luckily is super thick-skinned. My daughter knows about my sister's condition and has put up with a lot from her because of it. She finally decided that she was going to speak up about some things that really upset her. I turn the other cheek all the time, but it doesn't seem to me to be fair to tell my daughter that she needs to choose to do the same.
And I'm very uncomfortable with the idea of listening to my sister bad mouth my daughter --- also seems like a slippery slope to getting pulled in.
But perhaps there are options I'm missing....
I agree. It was invalidating to be expected by the adults in the family to tolerate my BPD mother's behavior and I didn't expect my children to do that.
It's the adult's role to protect the children, and once the children are adults, to allow them to protect themselves.
The nuance for me was finding the difference between respectful behavior to a relative and tolerating unaccptable behavior- and finding a boundary between them.
I can understant listening to a pwBPD's concern about a family member, if it was a genuine concern but with my BPD mother it was triangulation. It's also unethical to say unfounded negative things about another person and it is not being respectful to them or the person being badmouthed to enable that.
However, when dealing with a pwBPD, we also want to avoid fueling the drama. Sometimes the statements are about getting an emotional response. One option is to "grey rock". If you respond with emotion, or defend your D, or say why your sister is wrong about your D, it is adding fuel to the drama and in a way validating it. "Grey rock" is to not react and to disengage from the conversation in a non confrontational way.
In my situation, my BPD mother would "vent" her concerns to me about my sibling. I also knew she would vent about me to other people. This was Karpman triangle dynamics. I did listen to her for a while, assuming this was being respectful but them decided this was enabling this and so stated "I don't wish to discuss my sibling's personal issues, this is between the two of you". If she persisted, I found a reason to end the conversations "Mom there's someone at the door- I'll speak to you later" or change the subject. Eventually, not being a listener decreased her doing this with me. I then did this if she began to do this with me about other family members.
With my children, I wanted them to behave respectfully to their grandmother- to respect the relationship and because it was the decent thing to do. I also let them know they can have their own boundaries as teens and adults. One adult child felt comfortable with a relationship with her by text and phone (my kids didn't live near her). Another one, she did something hurtful to, and that child decided to not have contact if she called or text. In her presence, the kids were respectful.
The "turn the other cheek" is about non- retaliation with hurtful behavior. It doesn't mean one has to allow a person to be emotionally, verbally, or physically abusive, or have any self defense, or to expect a child to do so. To me, it means that if BPD mother says or does something hurtful, I should not do something hurtful back at her, but I can have boundaries and so can my children.
Not triangulating with my mother didn't mean I didn't ever discuss family members with her but if I got the sense she was asking me to speak for them, or get them to do something she wanted, I would turn it back to her saying "I don't know, it would be better if you asked them, or I don't know, this is between you and them.