The sad fact of Alzheimer's is that your grandmother will continue to deteriorate so this is really only one of many stages. Try to take some comfort in the fact that the situation may well resolve itself as your Oma continues to change.

In the meantime, try having a caring conversation with your aunts even if it's difficult. It sounds like they have gone off the deep end a little if they think you will put your own needs before your grandmother's. However, I can attest that watching your mother suffer from this miserable disease does a number on you. I've had some ugly squabbles with my siblings on occasion over my mother's care, not because we don't love each other or believe we all want the best for my mother, but just because it's so very hard when you really disagree with whatever someone else thinks is the right thing to do. And there usually isn't one clear answer.

If this has happened multiple times, I do kind of understand your aunts being concerned. It's normal to try to stop whatever is upsetting your parent in that kind of situation. So try to cut them some slack. Ask your aunts for suggestions for visiting, see what they think of you visiting separately from your mother, wearing glasses and a wig or hat, etc. Ask them if they have any ideas that would let you help facilitate her care by speaking in German.

Alzheimer's is a miserable, horrible, awful disease. I'm so sorry you're having to watch someone you love suffer from it.