WTBH, I'm fairly certain you can get a cheap "Nanny Cam." They can be disguised in almost anything. Set it up in the living room...or whichever room the AH sends time drinking in when with the girls...and let it run.
AS for not emotionally believing that you don't deserve this treatment...that comes from being raised by BPD Mom. I think I would really start working on this aspect with your therapist to truly heal. Also, start embracing yourself...that scared little girl you were as a child living in chaos. Start nurturing Little WTBH and forgive yourself. You didn't do anything wrong, but sometimes we take on responsibility for our parent's actions and treatment of us. And start looking at yourself as a SURVIVOR!!! Do you have any idea how strong you are...even as a small child to live through the chaos???? THAT is what you need to believe...not the lies and blaming coming from ill minds.