Both my grandparents have diabetes and other health problems. My grandma is getting weaker by the day. She has a bad back and horrible pains in her abdomen constantly. My grandpa is on oxygen and has a catheter and is even weaker then her. He NEVER gets off the couch I'm surprised he doesn't have sores and can even walk when he does get up(which is hardly ever). He constantly is having her do things for him he can clearly do for himself and is VERY mean about it. He will call her out to living room at least 30 times a day just for random things he could definitely do. I try to help when he call hers Ill go out instead and ask what he wants but he always says "I don't want you. Get your grandma" Her health is dwindling as the days go by. I'm scared he is going to end up killing her! What can I do???
I'd just add: you could help your grandmother by checking that she is being looked after medically. If you find she hasn't taken the time to get her back and tummy examined, perhaps take her to the doctor? - whatever's necessary and appropriate.
And this is your time to learn some really essential things that will be useful for your whole life. First, it takes two to tango: your grandma has a role to play in whether or not someone else runs her ragged, whatever generation she comes from. And two, other people's relationships are always a mystery from the outside. It may look terrible to you, but this may be the way they stay deeply connected with each other after all these years! Maybe if your grandpa STOPPED calling on your grandma all the time, THAT would do her more harm than being left in "peace" because the way he needs her has been so important to her all this time. I'm not saying that's how it is. I'm saying, we can't know. But they keep choosing this way of interacting -- both of them.
You can do some things to make it lighter, like fuss at your grandfather if he yells. But if it their usual family dynamic, I would let them work it out.