Spouse's Ex is uBPD and Abusing Children, Spouse is Passive About The Abuse

[WanderingLove]

Seeking Advice: Supporting My Husband and Stepchildren in a BPD Family Dynamic
Hello All,
Thank you for being such a valuable resource. I’ve read extensively here and in books, but I need advice on a situation I haven’t seen addressed.

Background
My husband’s ex-wife is undiagnosed BPD (uBPD), and while my husband is kind, caring, and insightful (he’s a therapist), he is incredibly passive about protecting his two daughters from her emotional abuse.

When we met in 2018, I noticed the mother’s controlling and intrusive behavior toward the kids. For example:

She called the children up to 12 times a day when they were with him.
She guilted them into staying on the phone by saying they were “ungodly” if they wanted to hang up.
Exchanges were chaotic, filled with her manipulative and gaslighting behavior.
Despite this, my husband encouraged the girls to be polite and obedient to her, even when she was clearly being abusive.
The Move and Parenting Plan
After we married, his ex-wife announced she was moving to Alabama. My husband agreed to the move, and we relocated to Louisiana to be closer to his family. However, she changed her mind at the last minute, forcing him into a 4-days-a-month parenting plan since he now had to travel 2,500 miles to see his kids.

I expressed my fears in writing about how unsafe the girls would be in her care and urged him to seek therapy to understand his passive and permissive approach. He always said he’d “think about it” but never followed through.

The Current Situation
In recent months, both daughters have disclosed severe emotional and psychological abuse at their mother’s home:

Screaming, raging, and controlling behavior.
Throwing away their clothes in anger.
Denying them contact with safe people, including the ability to call the police.
The older child has even attempted suicide. The children are now begging their father to fight for full custody. However, my husband says he will only pursue 50/50 custody and insists that their mother is “just sick” and not intentionally harmful.

He has a lawyer and is pursuing 50/50 custody but refuses to read books, follow advice, or disclose the full extent of the abuse to his lawyer. Meanwhile, I’ve read books like Bill Eddy’s Splitting and have outlined strategies, but he won’t engage with them.

History with His Ex-Wife
He was married to his ex-wife for 15 years and endured significant emotional and physical abuse:

She ran him over with a car, scratched, bit, and hit him, and took the phone out of his hand when he tried to call the police.
He never filed charges, and he never initiated the divorce; she filed after he emotionally withdrew from the marriage.
Since their divorce, she’s remarried and divorced within four months, had multiple boyfriends, and continues to stall parenting negotiations.

My Concerns
I’ve told him I cannot stay in the marriage if he doesn’t get help to understand and address the core wounds that made him tolerate years of abuse and continue to freeze in the face of protecting his kids.

I’ve set a boundary that I won’t be available to him until he starts therapy, but after a week, he says he’s too overwhelmed to find a therapist or take action.

Meanwhile:

I’m states away from my support network, raising his nephew, and only able to contact the kids when they are with him.
The denial, passivity, and protection of his ex-wife are causing resentment and making me question if there’s any hope.
Seeking Insight
Has anyone experienced something similar and seen meaningful recovery from passivity like this?
Are there strategies to help someone like my husband recognize the need for therapy and take decisive action to protect his children?
Is it reasonable to have hope for our marriage and his personal growth if he continues to freeze in the face of this trauma?
Thank you in advance for your advice, stories, and insights.