Well, maybe a place that's close enough by that you can sort of keep your eye on their well-being, without having to live with the noise/chaos/drama on a day-to-day basis, might be a very good thing to consider. You could research what services might be able to stop in and do some of the things you've been taking care of. It sounds as if grandma has sort of settled into this routine and escapes when she needs to. But she should know about Al-Anon and other sources of help.
I don't know how bad the "verbal abuse" is, or how much that might be harming her, but if you could help put her in contact with your local women's shelter, they might be able to provide her with some assistance, too.
Hope you will stick around here--this is a great place for support.