I'm with the last to responses in this -
my wife and I have three daughters, two from her first marriage, and one from ours.
As far as I am concerned, I have three daughters, and they each have two sisters.
It's how you feel about them, and how they feel about each other that matters - itls never been an issue for anyone in the family - no differentiation at all from amyone to anyone - and it's our view that matters.
I(f other people want to be 'half' this or 'full' that, fine - but I don't make those distinctions.