Ds is 8 and his dad passed away not long after he was born. I'm remarried and we have a daughter. It never occurs to me that they are half anything. They are brother and sister and that's it.
I guess it isn't odd if you grew up in different homes, but it just strikes me as a little strange when someone labels their sibling that way. There's nothing wrong with it, of course, I just wonder if people don't feel as attached to the brother or sister that has a different parent?