Twins. Logical puzzle?

[chidambaram k]

Two girls are born to the same mother, on the same day, at the same time, in the same month and year and yet they are not twins.

[joker]

As you have told already ,they are girls only.....and not anything else....
how many of them were bron along with the girls?Give the details .....so it is clear that the girls were born with one or more......