grandchild ?at risk in mother's verbal aggression towards farther

Not enough info

I think it is more than likely the actual shouting that upsets the child rather than the content.
Not nice either way.

Doesn’t sound like OP is grandmother. Difficult to say anything without knowing more.

Definitely can’t comment with so little information given.

Are you the grandparent? could you sit down with the parents and have a talk to them. They need to be aware how their behaviour is affecting their child.
Is it possible for you to take the grandchild to yours for a break or go out shopping for a few hours. Just something for the grandchild to look forward too?
You may well be told it’s not your business but make it your business for the child’s sake.

My goodness there isn’t much here to go on
If you’re the grandmother maybe you can give a bit more information are?

Aw, I feel so sorry for kids stuck in a horrible angry household.
You don't say what the relation the mother is to you. If it is your daughter then please have an honest talk with her and try to get her to go to counselling. If it is your son in the relationship, then have a talk with him.

You will most likely be told it is not your business, but just let them know you are concerned for the child, offer to babysit while they seek help.

good luck.