Watching a struggling, bullying carer

Hello, I visit my Mother-in-law regularly as she is cared for at home by Carers along with her husband and daughter. The daughter visits 3 x weekly. I am very worried about the treatment my Mother-in-law receives from her daughter. Mother and daughter have always had a fiery relationship. Now that my Mother-in-law is bedbound and blind she is very dependent on others.
Her daughter is very argumentative, which I have to accept. What I am really struggling with is her aggressive, bullying attitude towards her Mother. My Father-in-law backs his daughter up.
There is no physical abuse that I am aware of but the regular verbal assaults are often terrifying. All my conversations with my visits are recorded on a camera and I am often quizzed about this. I am beginning to notice some controlling elements as I am rarely left alone in the room to have a conversation or give a meal to my Mother-in-law. I have a very good relationship with her and enjoy my visits as she comes alive and is often quite lucid.

The visiting carers are amazing.

Unfortunately my sister-in-law and Father-in-law refuse any support, they say they don’t need it and it won’t help. They feel this is just a nasty vindictive person they are caring for.
Please can you advise me on how to go forward with this.
I feel I need support so that I can manage myself in this situation.

Thank you in advance.

You can contact the local adult safeguarding team and say you are concerned re emotional abuse, this can be done anonymously. You could send them copies of the video footage too, though that of course would implicate you as the person reporting the issue and could result in the family no longer allowing you to visit.