My twin correctly pointed out that I didn't mention it being 'our' birthday on Sunday. I'll share a little anecdote about our birthday. It's funny when you are a twin, it takes you forever to stop saying 'our' for everything... and then you still say it much of the time.
When we were in grade 8 our Dad and Stepmom got pregnant. The baby ended up being born two weeks late. On Our Birthday! So we got to name her. Kind of like a 14th birthday gift to ourselves. Sooo, we named her a combo of our two names. My name is Tara. My twin's name is Tena (pronounced 'Tina'). Our new baby sister: Teeara, obviously. Pronounced 'Tiara', but needing the unique spelling, we insisted, that would make her name truly derive from our strange combo. And the double 'ee' to make sure people were clear on how to pronounce it.
It seems very normal to us all now, but there were family members who thought our parents were mad for letting us name her, and Teeara herself went through a rough patch over it in her teens. I think we are well forgiven now. She can at least be grateful our parents drew the line at letting us give her the middle name Maria. We wanted to nick name her Tia, and at 14 thought Tia Maria would be a seriously cool and sophistocated moniker.
So, yes, Sunday it's all three sisters' birthday. (And mother's day of course.)