Just by step mum's name. I didn't think about using anything else tbh, as my DS is the first grandchild so she was just known by her first name to me and my eldest brother. But i think when my DD comes along I might ask her if she would like to be known as nanna 'name' or something instead. I feel a bit bad for never asking her, all the other grandparents names were sort of just assigned depending on what *their* parents were called, but i call stepmum's mum by her first name, too.
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