Hi bugwaterguy;
Couple of general thoughts come to mind:
If she's the one saying words about wanting divorce... don't help her.
Often, members have partners who say lots of words about wanting divorce, but the member, like you, wants to keep the family together. Weirdly, sometimes there is a (perhaps subconscious) thought of "I must help my partner with figuring out the steps of divorce, because she just can't seem to figure it out on her own, and I'm a helpful person, and maybe if I show support and help her with what she wants, we'll stay together". (Not saying you're doing this, just saying it has happened before)
Consider, instead, letting her succeed, or fail, at trying to divorce, on her own. If she "just can't figure out how to write a parenting plan", or "has no idea how to get a lawyer", or "wants out and away from you, and you're the bad guy for not helping her file papers"...
let her succeed or fail at those things on her own.
Let your own actions match your own values. You currently want to work on the marriage. So, don't do things that undermine what you say and believe you want.
I think many pwBPD can "talk a good game" about stuff that "sounds serious" to us, yet, when it comes time to use executive function to actually DO a process... they really struggle.
If she wants the divorce, she must figure it out on her own. And, conversely, if she is in fact capable of following the steps for divorce, there isn't much you can do to stop her.
...
I would also plan for the worst and hope for the best.
It is completely possible, "legal", and fine, to
both want to stay in the marriage and to try some stuff to make it work,
AND at the same time to come up with a custody arrangement and parenting plan that will be best for your kids (as you mention, you suspect she may lash out at them if you aren't there... so they may do better with more time with you).
At this point, don't share your plans with her. Get some plans together privately, on the side, and have them ready for the "worst case" scenario that she actually follows through with filing for divorce. You want to be in your strongest possible position to protect the kids if she does that. If she doesn't file... that's fine.
Consider having a couple of initial consultations with local lawyers. Give them the nutshell version, describe any documentation you have, and they will (often for lower cost or free) let you know what you can expect in your area. That can help you decide how long to fight for the marriage, and at what point your kids' needs become higher priority than the marriage, and you have to file first to protect them.
...
During divorce proceedings - is it relevant to bring up BPD with lawyers or a judge?
Even if she had an airtight 110% diagnosis on paper... probably not, unless there is 3rd party documentation directly linking her diagnosis to specific abusive/damaging actions towards the kids.
I would see it as a distraction and it might even work against you ("See, bugwaterguy just wants to throw mud and label his wife... they're just the same, they both deserve each other").
I'd instead focus on documenting patterns of behavior that negatively impact the kids.
Has anything she's done impacted the kids' schooling?
Have any neutral 3rd party professionals (counselors, therapists, doctors, teachers, coaches, etc) documented any concerning things she's said or done to them or to the kids?
...
Focus on areas where you can have maximum "payoff" for the effort.
Focusing on labels is generally not a winning game
coming from the ex-partner.
Even coming from professionals on the stand, a label doesn't mean as much as we want. I would see that area as minimum payoff (if any) for the effort.
Focus instead on getting the absolute best custody and parenting time arrangement as you can, as soon as you can, even/especially if it's "temporary orders". My gut feeling is that's where you'll have most payoff for effort.
Focus on protecting yourself and never letting her goad you into an outburst. Consider carrying a pocket recorder (don't let her know) to cover your bases, so you have documentation that you aren't the aggressor.
See if you can get the kids into counseling/therapy and get an established relationship with a good professional. You don't have to wait for a divorce to happen to do this.
If things do go to court, be focused on solutions for your kids. Always have a proposal or two ready; don't waste time on how "she always... she's just like this... she's the reason for the problems...". Laser focus 110% on the kids and their needs, be "the guy who really doesn't want to label people". Do present patterns of behavior that impact the kids.
...
Just a first go at some ideas...
Let me know your thoughts --
kells76