Oh, Angela...I'm so sorry.
Not just that you're hurting, but to hear that you're losing your grandmother this way. This part is so much harder than the actual dying part of it. Some of the things that came out of my granddad's mouth have scarred my aunt forever; she had always been his favorite, and in the end, she became his target. And she was nearly 3 times your age when it was happening. You have every right to be mad, and it's good that you're letting yourself feel it and vent.
You don't deserve any of this, and you shouldn't have to be the responsible one at your age. But they're your family, and it's obvious you want to do whatever you can. If you didn't, you wouldn't have moved in in the first place.
SO ON THAT NOTE:
What you need to do, right now, is call up your county social offices, and ask to talk to someone about senior services. Explain that you are an "only" family member dealing with your grandparents aging issues, particularly that your grandmother has Alzheimers, and that you are recently injured, overwhelmed and need help ASAP! It may take some phone calling, but there is help out there for you.
In some parts of the country, they'll send a person out to meet with you; in other places, you have to go to them.
If you have to go to them, go the first time WITHOUT your grandparents, so that you can explain to the person--usually it will be a social worker, but sometimes it's a nurse or a psychologist--what your family situation is, and what the problems you're encountering are. Be honest--don't leave out the name calling and the abuse. It's symptomatic of her disease process, and the worker will need to know about it. Then you can work out how to arrange a meeting for your grandparents.
If they will come to you, make sure that you are able to go somewhere--even if it's out in the garage!--so that you can speak with the worker privately about the issues I mentioned before. Coming to you has the advantage of a first-person viewing, though, so if they will do that, I'd try for it.
Most counties have programs that can help you--home health, home care aids, meals-on-wheels programs, senior activities or adult day care placement, all kinds of things that you need, if not now, down the road. The sooner you get into the system to get help, the easier it will be down the road as you need more support.
Feel better soon, good luck, and God bless, sweetie.