Edited to take our recognizable detail.... Really struggling with my UDS son and his pwBPD soon to be wife.
She emailed to cut contact for both of them - before their wedding. But he has had issues with unhealthy relationships for years. It has been a decade of chaos.
My spouse and I are doing well now, therapy and the peace of no contact. I do wonder if it will be possible to find a positive way forward with them in the future. 

Hi Wantmorepeace,

Your name says a lot.  Since you're talking about a sibling (I'm guessing a sister), you've had to deal with BPD behaviors for most of your life, correct?  My guess is that you're tired of the negativity, the drama, the false accusations, the blaming, the endless strife, the grievances from decades ago, the toxicity.  My other guess is that you're sick of a family dynamic where parents or other family members are enabling your sibling's behaviors while expecting you to be the bigger person and put up with it all.  Basically they want you to take the negativity, which is damaging to you.  And yet you feel guilty, because you want to love your family and make everyone happy.  Does that sound about right?

A period of no contact would be for YOU.  That way, you would get a break from the negativity and get back to your normal self.  My guess is you want some peace, right?

I'd advise, if you need a break, take it.  Don't explain yourself, just do it, because you deserve it.  Get busy living your best life.  Now maybe your relatives will try to meddle and urge you to contact your sibling--that sort of thing happens to me sometimes.  I think I might say something noncommittal, like "Maybe later."  But I'd underscore, you don't have to justify yourself.  They shouldn't be meddling in the first place.  This is between you and your sibling, and you are entitled to take a break if your sibling is too negative/disruptive/needy/accusatory/dramatic/volatile.  You are NOT responsible for your sibling's emotional welfare.  If the family pesters you further, then you could say that:  "I'm not responsible for my sibling's emotional welfare / I couldn't fix their life even if I wanted to / My sibling's problem is not my problem / I'm sure they can handle things themselves / I don't want to meddle."

As for the BIFF formula of communication, I think it can help in interacting with a high-conflict person, though it's probably best suited for written correspondence.  An example might be with ex-spouses, who need to correspond regularly about logistics regarding children and visitation.  BIFF stands for brief (as short as possible), informative (sticking to facts), friendly (cordial and respectful) and firm (leaving little room for debate).  In other words, you avoid emotional content, and you stick to business.

However, if you are thinking about using BIFF to explain why you want to go no contact, I think that probably isn't a good idea.  Why?  Because your emotional state--feeling traumatized / tired / exasperated / guilty / dragged down--is not a business topic, it's personal.  Personal issues don't belong in BIFF communications in my opinion.  Explaining why you need space and getting into details would sound more like JADE to me.  JADE stands for Justify, Argue, Defend and Explain, which we learn on these boards is to be avoided with pwBPD when they are dysregulated.

In person, I think BIFF might look like treating your sibling as you might a colleague you don't particularly like, but you have to get along together to get your work done.  You could be cheerful (i.e. friendly)--"Good morning.  Nice to see you." You could be respectful--"Thanks for coming."  But you don't offer any revealing personal details, and you stay neutral emotionally.  You keep everything professional.  To continue the analogy, as a business executive, you're BUSY.  You need to wrap things up quickly so you can get back to your life as soon as possible.  If you keep visits and phone calls short and sweet, there's less possiblity for drama or a meltdown.  This might sound like, "Sibling, I'm in a rush, nice talking to you, bye."  By the way, "I'm in a rush" is my go-to excuse.  It works because there's no personal information there, but it's true, and everyone can relate.  Alas, my "in a rush" is usually to get to the bathroom, but people don't need to know that . . . my point is, less is more here.

Hi thankful person, good to see you.

That awareness you’re describing, especially noticing the discomfort instead of reacting to it, is a big shift. It may not feel like it, but that’s the work.

A simple next step is just staying with it a little longer each time, without fixing or people-pleasing right away.

If you want to share, what does that discomfort feel like in your body when it shows up?

Hi bpdUDS, just checking in on you.

You were carrying a lot here, especially with the wedding situation and stepping back from the chaos. That’s not an easy place to land as a parent.

If you’re up for it, how have things been since then? Has anything shifted with your son, or more on your side in how you’re handling it?

Hi Janine52, just checking in on you.

You shared a while back how exhausted things felt, being bombarded with messages and trying to hold everything together. That can really wear a person down over time.

If you’re up for it, how have things been since then? Has anything shifted, even a little, or are things feeling about the same?

Hi Pushover_Pleaser, welcome. Glad you’re here.

That’s a lot to carry, especially with the push-pull from your sister and the family pressure around it. It makes sense your anxiety is high.

What stood out is you’re seeing it clearly. You can love her and still protect your peace, even if others don’t agree.

Keeping it simple can help:

   •   focus on what’s healthy for you
   •   limit what you share

If you want to share, what kind of contact feels manageable right now?

Hi wantmorepeace, great to see you.

That shift you’re describing, focusing on what you want instead of their reactions, is huge. It may feel simple, but it’s a real turning point.

And needing to remind yourself is part of it. It takes practice.

If you want to share, what helped it click yesterday?

Hi Orphan, welcome-glad you found your way here.

That kind of dynamic wears you down over time-having to filter everything you say because it might get twisted or shared. It makes sense you’ve pulled back to protect your sanity.

What stood out is that you’ve found a way to hold both truths-you’ve forgiven her, and at the same time you’re keeping distance. That’s not easy, but it’s often what stability looks like in situations like this.

From here, keeping it simple and consistent can help:
   •   limit what you share (low-information contact)
   •   expect patterns, not change
   •   stay anchored in your boundaries, not her reactions

If you want to share-what tends to happen when she crosses that line now?

Hi marchstar, welcome-glad you found your way here.

That’s a heavy mix-BPD plus trauma from an abusive relationship. Makes sense you’re looking for ways to support her without it overwhelming both of you.

You’ve already done a lot by educating yourself. From here, keeping it simple can help:

   •   DBT (skills for regulation and stability)
   •   Trauma-informed therapy (at her pace)
   •   For you: boundaries + validation (support without taking it all on)

If you’re open to sharing-what kind of support is she getting right now?

Hi and welcome - glad you’re here.

Quick note: I saw this got posted a few times, so I cleaned up the duplicates just to keep things tidy. This thread is a good place to continue.

You’re on the right track looking for DBT-based dual diagnosis programs. And if local options are limited, virtual can actually work really well too.

Hopefully others can jump in with some good suggestions.