Hi CC43 and welcome to the group

It must be painful and frustrating to watch your SD26 self-destruct over and over, especially when it seems like she's had every opportunity to get help.
So much of what you describe sounds familiar: anger and dysfunction, verbal abuse of loved ones, extensive negativity, inability to let go of the past, blame... you're in the right place if you're coping with a family member with those traits.
One thing that comes up across all the boards here (whether your pwBPD is a child, parent, partner, ex, sibling... any relationship) is that the tools and skills for coping with a pwBPD are nonintuitive, often opposite of what we'd "normally" do, and must be learned and practiced.
After multiple suicide attempts, she seems to speak more frequently of wanting to die, and though it's a cry for help, sometimes I wonder if she's "weaponizing" her disorder to get what she wants (financial support and "reparations"). Her father always swoops in, to save her life.
Her father is your husband, right? Am I reading you correctly that the two of you are seeing the situation differently? Were you more on the same page in the past?
How many times would you say she's made suicidal threats or statements, so far -- like single digits, or more?
Do others know how to handle and de-escalate threats of unilateral assured self-destruction?
What has been tried in the past -- have you ever called 911 or crisis units?
Sorry for so many questions, just a couple more: where does SD26 live right now, and is SD26's mom involved?
...
Family structures where there are parents, stepparents, stepkids, and BPD, can be extremely stressful -- I do understand. There's not only getting all of you through SD26's latest crisis, there's making things more workable long-term. I know in our situation (my H's kids' mom has many BPD traits, and her husband has many NPD traits), I would not have made it this far without an individual counselor, a marriage counselor for me and H, and these boards. It takes a lot of support to make it.
What does your support system look like right now? Have you and your H done any counseling, either separately or together?
And have you heard of NEA-BPD's
Family Connections program? They now have two programs, one for if your family member has BPD/emotional dysregulation, and one for if your family member is suicidal. They're a reputable organization and the FC programs are free. If you haven't tried it yet, take a look, and let us know your thoughts.
Keep us posted on how you're doing -- hope you get some peace and downtime this weekend;
kells76