Mom is in 5 day respite for the third time. Dad keeps taking her back home within 1 or 2 days! How do we stop him?

She's safer w/out evil NPD him! He is a bully. Verbally and emotionally abusive. Selfish. Only wants her home so HE is not alone. I moved in and out so many times in the past 2 years due to his abusive behavior it's redic. I am with both of them 24/7 cooking, cleaning their huge house, bathing, cleaning and dressing and undressing Mom while getting punched, bitten and all when her disease makes her fearful, the response is violence. Ok. I am doing laundry, grocery shopping, etc. enabling them to stay in their house. I get it. It's her disease. It's ok. HE is the problem. The minute I arrive, he trots off to Home Depot today, the bank tomorrow, the post office the next day, disappears for hours and returns to berate me if I don't grant every wish he demands, or have moved the toaster to a safer place, etc. "This is MY HOUSE" kinda crap. Suggestions are not an option. He sees it as lack of CONTROL and loses his on me.
"Get the out!" So, I leave only to be sucked back in to return after he realizes how good he had it. He promises to change. I know him better but am more concerned with her safety than my emotional abuse. I've had a lifetime of it from both of them. Mom doesn't recognize me, so her NPD distain for me is, for the most part, gone. I feel so sorry for her and have been able through years of counseling to rise above the lifetime of abuse, to do the right thing for her. He is the worst of the worst kind of selfish, unaccountable Narc. Beat me regularly growing up, often at my Mom's request...then "That's enough" from my Mom would end it. I have one Golden Child, first born only son brother and two younger sisters. I was their second child and told from a very young age I was "a pain in the a**" and was supposed to be a boy, John Charles (!) instead of a girl. Sick 💩.
We were " Eddie Jr and 'the girls.' "
Still, "Honor thy Mother and thy Father" resonates with both my first sister and I. Not "the baby." She and #1 are Narcissistic apples from the tree. We two middle ones do the most altruisticly. My sister has a grandchild with Cerebral Palsey she cares for while my niece works, but she is always there from the "administrative end." A tremendous help with getting Hospice, respite, medical intervention, etc. I do the hands on.
I have my own home, 40 miles away from "home" am retired, financially solvent and content. My 3 birds are fully grown up and happily out of my nest. I have friends and a life. I set everything aside to care for them, only to be discarded when Dad's authority gets challenged in even the slightest way. He's actually juvenile about so much!
Bottom line is...
What does one do when the Chief NUT is running the asylum?!
How can we keep her safe - away from him, if he still is able to upset the applecart and reverse any action we take to protect her?
For perspective:
The last time he "GTF outed " me was when while I was washing up getting dressed for the day and came downstairs to find my Mom halfway down the block in her pajamas, "walking my dog" on a rope (!) while my Dad stood at the end of his driveway with his hands in his pockets just looking at her go!
My reaction was, Dad! What are you doing? What if the dog pulled her down? (90 lbs is Mom) or what if he pulled her into the street and a car came?! Or what if the dog got loose and she tried to run after it and fell?! (My Mom is small, but strong with no physical illness at all!)
His reply:
"What, if, what if! If you don't like it, GET THE OUT!"
I was on day 75 of 24/7 this last time. He didn't have to say it twice.
I didn't say anything. I left bag and baggage - again - this is one week later..."he can't handle it, your mother needs to go somewhere" then jump thru hoops to find a respite and there he goes again
Taking her back home. I'm not able to do anything more for him. My sanity at stake. Enough is enough for me. What to do now?!! I'm at a loss.