Speaking as someone who shared a name with both my grandmother and a great aunt from a different side of the family, I know all too well how confusing this can be. We solved it by using my middle name, which nobody else in the family had. Perhaps that might work, especially as it has no associations with elder/younger, junior/senior, big/little, etc. that might not quite apply or cause the named-for character to be extra sensitive about any tags or diminutives.