I have four grandparents (you know, just like everyone else). None of my grandparents are themselves twins. All of my grandparents have twins-siblings.
All of them.
Is that weird? I still have to count the size of the group, but regardless, I think it is at least a little odd.
ETA: Okay, yup, that's odd. But I made an error. My maternal grandmother was half of a set of twins.
Paternal grandfather is one of 6, fraternal twins are two of them (girl and boy). Woman wound up in sanitarium for mental problem. Man died comparatively young for our family (in his 40s or 50s, IIRC, in a group of people commonly living to 80s).
Paternal grandmother is one of 3, not sure if they are fraternal or identical twins. Definitely both women.
Maternal grandfather is one of 14. Male twins.
Maternal grandmother is one of 7. Twins include her and a twin brother who died in 1920; I heard the story that he died of the Spanish Flu.
Total group size is 30, of whom 8 are twins. That sort of defies belief, actually.