Hi Maiden7, panda said it all very well

welcome to a group of people who have also felt relieved to put a description to some really tough behaviors. I still feel "new" here so you're in good company!
My husband aka DH has 2 girls SD (stepdaughter) 11 years old & SD9. DH & I have had a really good marriage counselor for a few years which has been a HUGE help, I highly recommend finding a counselor for yourself. It's made an even bigger difference for the kids, especially for SD11, to have their own counselor. This only happened after 6 months of legal shenanigans but if that's what it takes, I really recommend getting a counselor for the kids too. Tip: find (or agree to) one who is in a group practice (i.e. maybe has a supervisor); that way they're less likely to get snowed by BPDx's behaviors.
Lived & Learned will probably recommend a book called (I think) The Power of Validation. It is geared for parents of kids up through high school but it should be applicable to any age.
That's the nutshell version; again, welcome! You are definitely not alone in this.