Tolla, that is because there are duplicate profiles of your grandparents:
"A merge should be done when two profiles represent the same person."
I proposed the merges of both sets of duplicate profiles. At the time you are completing the merge of your grandfather's profile you can choose the correct name for the merged profile. This way there will only be one profile representing your grandfather and the profile will have his correct name.
Come back to G2G if you need any further assistance.