My parents have been married for over 35 years. My mother is a narcissistic abuser and other than 2 text messages per year, I have no contact with her. She was awful to my father and he had planned to leave her as soon as I was independent, but for whatever reason he didn't have the strength and aged 70+ he told me there's no hope now and he just has to wait for her to die so he can live
I don't blame him for feeling like that.
Since going NC with my mum I have noticed a few things which concern me. My dad barely speaks on the phone to me anymore. On the rare occasion that he does, I am on speaker phone and I can hear my mother telling him what he should say, which he parrots back to me. I receive text messages from his phone, but I believe it is my mother pretending to be him. The language is the same as my mothers, and the texts are sometimes the same abusive stuff I used to get from my mum (and except worded as "your mother and I think...") and I get messages about how wonderful my mum is. When I ask directly if it is my mother using his phone, I get a response back saying no, it's all from him.
He refuses to visit me without my mum, and on the rare occasion we are able to meet without her eg because I'm passing through their train station and he comes for 5 mins to say hello, he seems scared and unsure of what he can say to me. Sometimes he lets through tiny glimpses of what's going on but 20 seconds later he clams up, tells me to leave it and not to worry. I haven't gone through their train station since January so I haven't seen him for a long time 
He has no other support network, my mother forced him to cut off contact with his family 35 years ago. I have offered him many times to move in with us, we have a room set up for him whenever he decides he's had enough, but he won't take it.
Is there anything else anyone can think of that I could do to help him?