My friend, Totty, that lives only a few miles from me has Joy, littermate to my Princess. I have to admit we were a little disappointed that they don't seem any more interested in each other any other dog they encounter. They are both way more interested in capturing the full attention of any human they meet.
Heather (GreysAndMoreGreys) says they are both such divas they can't bear to share attention and still have a bit of old sibling rivalry going on.