No one has their own birthday in our family!
I have 1 Aunty and 2 Uncles (same family and years apart) all born on the same day which is also the day after mine. My other Aunty is a week before. My mum is the only child in that family that has her own date but even worse as hers is New Years Eve.
DH's neice was born on his 21st
Our DD1 was due on DH's birthday but ended up coming on FIL's birthday instead. Which is only 6 days before mine.
DD2 & DD3 share obviously as they are twins but were also born on DH's Uncles birthday and 6 days before our wedding anniversary.
DD1 gets to celebrate her birthday twice as we usually go out for dinner or lunch anyway for everyone else. DD2 & DD3 have a joint party and always will. They have their own friends and also joint friends. But will always have their own cakes.