Two girls were born on the same day of the same month of the same year
to the same parents, but thet are not twins.  Explain how this is
possible.

They are two-thirds of a set of triplets.


Cheers,

pafalafa-ga


P.S.  This answer is admittedly a brief one, but I trust it fully
answers your question.  However, if you feel you need additional
information of any sort, just post a Request for Clarification to let
me know, and I'm at your service.