uBPD brother, uBPD grandmother. My dad is either the "all-good" child with tons of

, or he has strong narcissist traits. My mom is codependent.
Me, I'm living 3000 miles away. Divorced from N/BPDx for 3 years, raising S12 on my own. This is kind of a big ramble, I don't know what I'm asking or hoping for. I guess I just want to get this out and try to understand it better. I've been leaning into the pain for a while now and maybe the next step is to just detach and let the pain start to scar up.
My dad and I haven't spoken for 16 months. It's a long story, not sure it matters. But the short version is that N/BPDx husband had a psychotic episode one night while S12 was with him, and he sent 100+ messages in 12 hours all night long, including messages to me and my dad. I called my dad and told him please do not respond, N/BPDx is having a psychotic break, he is dangerous. Messages from N/BPDx made me fear he was going to kill himself and kill S12, so it was a rather rough night to say the least. N/BPDx threatened that I would never see S12 again. :'(
This hurts to much writing it, even though it's been over a year... .I was crying on the phone, so scared of what was going to happen. I was on the phone all night with police, DV hotline, friends, then therapist, lawyer, on and on and on.
When I talked to my dad, I wanted him to protect me. Or at least fake it. He couldn't even do that. Two weeks earlier, a woman had been shot in broad daylight by her ex husband when he lost custody of their kids, right in front of school, 2pm in the afternoon before she was going to pick up her children. In the psychodrama of the night with N/BPDx, I couldn't keep that story out of my mind, and told my dad I was scared. And while we're talking, while I'm crying, he interrupts to say that he has to go. That uBPD brother was calling and he had to go.
Blink. Blink.
Later, we are back on the phone because there are more messages, very crazy, all from N/BPDx, and my dad tells me ":)on't tell your mother any of this. She cannot handle the stress." My mom has epilepsy, so he worries about her, but also she doesn't handle stress AT ALL. Very fragile. She's had an exceptionally sheltered life, and doesn't handle crises, even little ones. N/BPDx is way out of her league. I thought my dad was saying, ":)on't tell your mother about this until S12 is home safe and sound."
Eventually, S12 was returned. Then a month later, he and I fly across the country to a city 3 hours away from my hometown where my parents still live. My mom and dad come to watch S12 so I can attend my conference. Other stuff had just happened -- N/BPDx wrote a letter to the police in my home town saying all kinds of things about my parents being alcoholics, not to let them drive, plus a bunch of other wacky stuff. It was a crazy letter, very stressful nonetheless like these BPD scenes can be.
I realized that my dad hadn't told my mom anything. Nothing. Not about the psychotic night, not about the letter to the police. Meanwhile, during our visit, my dad sent my mom and S12 off on a dumb errand, then tried to tell me to keep a lid on the crazy, don't talk about it with my mom.
I guess I sort of grew up in that moment, because I saw who he really was. He wanted to manage the situation by getting me to be quiet, which is how he's managed me my whole life. When uBPD beat me up, my dad wanted me to be the "good" child and just roll with it. Don't complain. Don't tell anyone. Just be quiet and there now, aren't you a good daughter. Perfect daughter. Now I love you because you're obedient.
So I finally saw the dynamic. And somehow my dad can sense this. He has not called, written, or acknowledged me for 16 months. There was no fight, no words spoken, just me becoming aware. My mom now knows about what happened. She's in a hard place, too codependent to do anything about him, but aware enough to see why I'm so hurt. She visits fairly often, and has started to save money secretly, which she then gives to me. My dad bought uBPD a house, but won't help me with legal bills, and he uses money to reward and punish, but then says he is fair, has integrity, is principled.
I'm in a good place. I have never felt so strong and healthy in my life. Being able to see clearly how my FOO is tied to my r/s with N/BPDx was profoundly healing.
But I don't know what to do now. My mom asked me if I would ever let her and my dad come visit together, like for Christmas. I said yes, of course. But also told her I am not going to remain quiet when my dad acts badly. He can sometimes be very petulant and selfish, and has snapped at S12. I won't let that happen anymore. If he is rude to S12, I will stand up for S12 and ask my dad to apologize.
Both my mom and I know that won't go over well. We both know my dad will stay at the hotel room and stop talking to me. He doesn't have a whole lot of emotional maturity.
But I also know, because I was raised by a world-class codependent and am struggling with those traits myself, that I can address my dad in a way that makes him step down and re-engage with me.
Doing that, though, means what? That I am going back to old ways? I'm the peace maker. Once, when my grandmother was dying, uBPD brother stopped talking to me over some mysterious slight. He would not be at the hospital when I was there, would not gather with family if I was there. So instead of grieving for my grandmother and coming together as a family, he created psychodrama about himself. So I sent this amazing letter of apology to uBPD and then suddenly, with no words spoken, I am back in the fold and things are peaceful. That's how I roll. That's what my dad wants. That daughter.
I don't know what to do. I'm not sure if my dad is NPD, but my T says it's splitting hairs. To me, it matters because if he's NPD, it means there's no point. If he's just mildly narcissist, or the "all-good" child, it's like there's more room for me to assert myself and be accepted for that. Otherwise, if he's NPD, then forget it.
I feel like I've mourned my childhood over the past few years while healing from N/BPDx. I never felt safe as a kid, had a weak enmeshed mother, a uBPD brother, a father with no clue, probably narcissistic, definitely alcoholic. Like I said above, I'm in a good place. S12 is doing well after many hard years. But I have this hole in my heart.
What to do about the hole?