My Mother in abusive situation

I'm writing on behalf of my mom.
My dad (her husband) is emotionally abusive, I guess you could say. He's always had a temper and won't tolerate anyone talking back to him (or expressing another opinion).

An example: My parents were going to go to a movie. My mom had a note by the phone that she needs to call her doctor, but that particular doc is only in the office on Fridays. My dad said call them anyway today (Wed) and leave a message. She said it wouldn't do any good b/c she needed to talk to her in person to make an apt. He tells her to still call. She says again, it wouldn't do any good in this situation. And that she'll 'call when she wants to.'

He BLEW UP and screamed and slammed things and said "don't you ever talk back to me!"
She said "why can you say things like that and I can't?"
He said "B/c I'm the provider" and some other things, then "do you want a divorce?" and some other things I don't remember.
Then he left w/out her and said "Don't include me in your dinner plans" meaning no telling when he'll be home.
I also said something in the same capacity a while ago that was an affirmative statement like my mom did; was something like, "No, I won't do xyz"

So it seems like if you stand your ground, it's unacceptable.
Well they've mentioned divorce many times but right now my mom is diabetic and has had a kidney transplant, which is now failing, so she's on a list for another.

Her eyesight is bad and she has lots of dr apts and meds she takes. So it would be very hard to live on her own. I could help but I work less than part time (looking for full) and couldn't pay for anything. They're both living on social security and pensions b/c they're both retired. My mom and I figured out that she'll definitely be short on money and couldn't pay all the bills by herself.

She doesn't see a way out. Is there anything I can do or place I could go or resource I could look up b/c I don't have an answer. It's like she's trapped due to her health and money problems.

My dad has always been a dick and I know it's emotionally worn on both of us. I can't stand up for myself in front of him either b/c of all the yelling and cursing and slamming. He's never physically hit us but he's shaken me and used a belt on my older brother when he was young.