I thought you were kidding, or that it was something from The Babylon Bee.
Unfortunately, no, "nibling" is an actual word now.
I don't relish the visuals it conjures up.
And I always thought that we called these kids “Niblets”. My bad. Take me out behind Biden’s shed and burn my old Merriam-Webster dictionaries.
Oh, do it again, Joe. Singing “Feels so good”.