I totally understand why you'd want to step into the background and away from the potential disaster of a meet-up.  But it would be good to support your husband in his time of need.  Yes, if asked, he would probably say he needs you by his side even if the day doesn't go well.

I would caution you that it's very possible that his son will cancel between now and then, though of course it would actually be by his BPD wife's demands.  The impression we have here is that he's been trying to appease his wife, an impossible concept.  Let time reveal what happens.

Would your stepdaughter be there too?  She might keep things calmer or it might trigger his wife.  We're remote and can't discern how much of a good thing that might be.

If the visit does happen, whether at your home or in some neutral location (a park perhaps) do natural things families do... take photos of the kids, parents and grandparents.  Yes, even stepson's wife.  To lessen the risk of his wife's upset and/or control, let stepson use his dad's phone, or yours.  Or his sister can do so, if there too.  This way, once the day is over, the phone with many photos and clips of the grandkids will be in your hands, not locked away elsewhere as ransom at the whim of a volatile spouse.

As you can see, some advance strategy is quite helpful.

Not sure where to start. Just sad, confused and utterly broken as to why my mother never sought help. Tired of being crisis manager and sad it continues to tear our family apart. Feel alone and confused

Another piece of advice is that you are hurting a lot, and so are other members of your family. This is completely valid. My BPD mother went all out in terms of hurtful and damaging behavior- at a time when I was grieving my father.

I didn't go NC but I decreased contact- for my own emotional recovery. Neither you or the other family are in an emotional space to deal with your sister. That is OK.

I went to therapy. I recommend this for anyone dealing with a pwBPD. The counselor urged self care- turning the focus on me. It's also good advice to not make big relationship decisions when someone is in a state of feeling hurt and grieving. You may need the distance for your own well being, that is OK to do, but reacting, anouncing to your sister, - she's in a dysregulated state.

This is not about placating your sister, enabling her or giving her a pass on her behavior. This is about taking care of yourself however, you feel you need to. You don't announce to your sister that you are brushing your teeth, or going to the gym. These are self care things you do for you. Taking some time to yourself can be in this category: personal and private.

It may be that there can't be a relationship but by keeping your focus on you, taking the time you need to do self care- you will be in a better position to handle the situation however it goes.

From my own experience, there's no real damage control. I think it's a choice between consequences.

Going NC or not will not control what the pwBPD says or does. They can still go around badmouthing people, and continuing their behavior.

Although NC seems to be a more common phenomenon- there are consequences to that as well. It doesn't control the pwBPD's behavior. If the damage control is about ones own mental, emotional, physical well being- where contact is detrimental- then NC can provide damage control.

Some people feel more at peace after NC and some people do not. They may still feel some grief. NC doesn't need to be long term but reconnecting may feel more strained or awkward.

At this time, the decision is about your own mental and emotional well being. If you don't want contact from your sister, my best advice is to not anounce it to her, or anyone. Just do it. Don't initiate contact with her. If she calls, texts, emails, you don't have to answer. Another way to do this is what I call a slow silent "fade". Don't answer beligerant or insulting messages, or emails. Don't answer all of them. Maybe choose to answer on occasion.

Boundaries are about you. You decide on the contact you choose.

Don't do this to "teach her a lesson" - she's so dysregulated at the moment, this will only escalate the situation. Just silently decrease contact.

I'm not an advocate for blocking, unfriending, on social media unless someone is being verbally abusive and sending threats. If she is, then it's appropriate to do this. If not, better to just ignore (IMHO). For phone blocking- mine will just go to voice mail but the person can still call. If yours does that, this is an option to give yourself some peace and you can still see messages but the call won't disturb you. Otherwise, let her calls go to voice mail and choose to respond or not.

I have a (former I guess now) friend who got angry at me by association- not for something I did directly. She was already angry at someone else I am connected to, and so she unfriended, unblocked the entire group of us. I attempted to reach out to her but now I can't. I hoped she'd reconsider but now so much time has passed, without any chance to clear the air, it would be a huge mountain for her to climb to repair these relationships even if she wanted to. I don't know if she has BPD but it's all the more difficult if she does.

If you think you may want to reconcile in the future, LC- on your terms- how much you choose, without announcing it- leaves the door slightly ajar for that possibility.

What is the type of relationship? 
Sibling - younger sister

What is the status of the relationship? 
Currently NC, or at least very, very limited contact (8 months)

How is the current status working for you?
It would work fine except that she continues to attack, escalate, smear, and has done true damage to relationships and my peace of mind, as well as that of other family members.

What is the top challenge you face with your loved one?
Not understanding her end goal.  Sense that there is nothing that will satisfy or stop her in her campaign of aggression.

How would you categorize your loved one?
UBPD

What do you struggle with yourself?
Sense of loss because the relationship used to be good, but her behavior began when another family member died suddenly, so it is tied up in a whole overlay of loss and grief. It is bewildering and incredibly confusing that she went so aggressively on the offensive - literally taking steps to destroy relationships and reputations - at a time when everyone else rallied together to support each other.  I and others cannot stop fixating on her behavior, worrying about her, swinging between being in denial that she could take such a turn and being furious at her.  It is a distraction, has sucked up all the mental energy so that processing the grief has been pushed to the side, creates a feeling of constant alarm, fear and instability at a time when everyone wants to guard their mental health and move on and look to the future after this tragic loss of a family member.

What are your goals at bpdfamily?
So far, it has just felt good to have a place to write about what has happened and have the validation of seeing people's responses.  And to read the posts and see how much of the experience is similar to others.

I will always be hopeful. Right now, it's a matter of damage control and defense. Unfortunately. Everyone hopes this changes, but feels like she is the one in control of that.

This is a very good point. I am making assumptions but the more I think about it, the more there were signs. Nothing as intense as what is now happening, but it is on a continuum.

In my earlier years, I couldn't afford a new car - and not retired now either.  But as I drove away as the new owner, I always commented "soon I'll find out why it was sold".  One time it was even before I got home.  The A/C quit on me, a major gas leak.  The dealer had bought it for me at a dealer auction so there was no recourse, ethically I couldn't blame the dealer, he was fooled too.

Ilearned that lesson as a young business owner.  I tried to do everything myself and save money since it was just me at first.  But I eventually realized that the thing I spent 10 hours doing myself, I could have earned $200, 500, or even 1000 in that same time period...and I could have paid someone $50 to handle the thing that took me 10 hours.

I quickly learned to pay people what they're worth and to put a premium on my own time.  Everyone should know their values and plan life accordingly.

Oh, I can relate to your kid's husband, deciding that he would give up on buying the truck!  It's not worth the time or the aggravation.

Since I worked in finance, I have found that attributing a monetary value to my time has been helpful in making decisions.  In this case, I wouldn't only be evaluating the purchase price of the truck and the needed repairs.  In this case, I'd estimate the amount of extra time (and therefore emotional energy or mental bandwidth) I'd have to expend to deal with the difficult situation.  I'd think to myself, well this isn't like going to a dealer and buying a car, which could take an afternoon out of my day.  No, this would require talking about it, waiting for the title from the counterparty, all sorts of issues regarding the registration, past taxes, back-and-forth, the works.  My guess is that she'd delay, claiming to have lost the title or something.  I'd apply my conservative uncertainty multiplier of 5x, meaning that what should ordinarily take four hours needs to be multiplied by five times (i.e. meaning 20 hours to get the deal done), because of a difficult counterparty, the novelty of the exchange and the associated uncertainty.  And then I'd value my time at x$ per hour.  When I was younger, I valued my time at $100 an hour.  So this transaction would consume $2,000 worth of my life.  I think I'd pass, because it wouldn't be worth my effort!

Now that I'm more mature, I value my time and emotional energy at an even higher rate, probably $250 an hour.  That might seem high to you.  I guess what I'm saying is that I protect myself by putting a premium on my time for any "special" efforts on my part.  If you share that view, then maybe letting the truck go would seem like a bargain.

I guess that when dealing with pwBPD, there's no "winning".  She wins if she keeps the car, and she wins if you get the car, because she'll extract more money, attention and mental bandwidth out of you--you'll have bought the car twice!  Maybe your calculus is different, I get that.  But I suspect you know what I'm getting at here.