I know there is little I can do but do any of you have any advice? Is there a way I can help?
You know there's little you can do, but eventually you will get to the place where you know there's nothing for you to do here. This isn't yours. Might be a good exercise for you to ask yourself honestly why you are getting angry and seeking to act on someone else's behalf who hasn't even expressed a need or desire for help. Sometimes when trying to hold onto an attachment we know we need to let go of, we look for reasons to not let go.
Your wife's grandmother sounds not only perfectly capable of taking care of herself, she sounds like she's made a firm decision to actually do that, to remove herself from one situation and go somewhere closer to other family members where the situation would be better for her. Good on her, I say. At 83, it sounds like she's taking care of her own needs and making decisions not based in codependency or clinging to relationships that have proven no longer entirely healthy for her. So when you say "whatever they are doing, it simply is not right," you might learn a lot about yourself and which direction will take you toward full healing by asking what exactly you believe they're "doing," doing to whom, why it "isn't right," and why you feel you should intervene in any way in a situation this seemingly very independent grandmother has already resolved for herself.
“The desire to be loved is the last illusion. Give it up and you will be free.” ~Margaret Atwood
You can either be consumed or forged. It’s up to you; the fire doesn’t care either way.