Speaking as another shared-birthday bod - my brother and I were born on the same date, just two years apart ;) - when we were younger, we always used to share a party (but still with two cakes etc!) - once we got older, we tended to have one doo the weekend before, one the weekend after - but since we both got to go to both, neither of us complained!

Although I'm ashamed to say we totally failed to even meet up for a drink together this birthday or last, which was kind of bad given we were both in Oxford!