A man has children (and then grandchildren) resulting from his first marriage. He later marries again and has another boy and girl. How is the relationship between the children of the second marriage and the children (and grandchildren) of the first marriage correctly described? I can never seem to "get my head around" this kind of relationship. Many thanks for the help of any clear-thinking people out there.
the first children from first marriage and second marriage are half brother / sister to each other and the grandchildren would see them as half uncle / half auntie .
Half and half. If you have one parent shared with someone else you are a half brother or sister. If your parent married someone else who already has children, those children would be your step-siblings. That's the way I've always worked it out.
His children from the first marriage are half-siblings to the children of the second marriage and all children that are his grandchildren are cousins to each other, you could decide to call the grandchildren half cousins, but that's pointless really.