In the list of possibilities, you forgot offspring of someone who is getting married. Preferably not your parents after you were born, but second marriages happen.
And there is the peculiar possibility of former spouse, especially if the parting was reasonably amiable. (I like her, I just can't live with her.)
More possibilities
And there is the peculiar possibility of former spouse, especially if the parting was reasonably amiable. (I like her, I just can't live with her.)
And what about (gollum) Ring Bearer?