Welcome. You are in the right place and we understand. I am sorry you are going through this with your daughter. I'll cut to the chase and suggest therapy for you and or even you and your son- I am not sure of your finances/ health insurance especially during the pandemic. Helping yourself first is the key ( although it is counter-intuitive) .
Many of us here also go to 12 step meetings for family members ( al anon, nar anon, Coda, etc..) as these help us put the focus on ourselves. There are online meetings.
In addition, may I recommend you learning all you can about BPD by reading the suggested books mentioned in the library here. One popular book is " Stop walking on Eggshells"
Yes, many BPD don't realize they are ill and think everyone else is the problem. That in itself is part of their brain that does a malfunction, preventing them from having the insight to see they need help.
A link from this forum may help
https://bpdfamily.com/content/ending-conflict.
I am sure others will chime in, and please write back as you are able.