Barbara Wallraff’s May I have a word column in the Boston Globe tries to address It’s all relative. Specifically, what you call certain folks to whom you are connected. For instance, how do you “refer to your grandchildren’s other set of grandparents”?
Her favorite suggestion was “parallelogrands, ‘owing to the pairs’ literally parallel positions on one’s family tree. Variations might include parallelogramps and, well, parallelogram. Readers also recommended grandsisters and outlaws. A couple of decades ago, the wives of my wife’s brothers and I would refer to each other as the “outlaws.”
Wallraff’s readers contacted her to inform that “a Yiddish and Hebrew term for relationships of these kinds is machetun in the singular and machatunim or machetunim in the plural… Machetunim covers “all one’s relatives by marriage,” per the late New York Times language columnist William Safire, and its singular form can refer to a relative by marriage even as distant as “your spouse’s mother’s second cousin.” I LOVED Safire.
The writer also discovered on her own “that Spanish has consunegros to describe some or all relationships of this kind, Italian has consuoceri, Greek symbethèra (or συμπεθέρα), Russian a gazillion specific terms categorized in a way I don’t understand, Tagalog magbalae, and English-speaking cultural anthropologists affines.”
Para, perhaps
Mushing all of these suggestions in my head, I think I’m going to opt for para- as a choice. It’s a nod to the parallelogram, but that has too many syllables! Para- means “alongside of”, or “closely related to”, among other things.
I’m thinking about this specifically because I was looking to find a tidy definition of a guy who died this year, who I’ve alluded to before. I was very fond of him. His name was Jack White; no relation to the guy from the White Stripes. He was the husband of my wife’s first cousin, Diane; yes, Jack and Diane. It was she who got me some of his cool baseball books.
In fact, I had envisioned Jack, my late father-in-law Richard, and me going to a major league ballgame one of these days. We always talked about the game at the Olin family reunions. So I’m trying on para. Jack would be my para-cousin. Or maybe para-cousin-in-law because he was my wife’s paracousin, or cousin-in-law?
Or maybe just cousin, because it’s what I call my great aunt by marriage’s nephew. Cousins cover a lot of ground.
I suppose I should not be ungracious. Still, there ARE some things I just don’t want for Christmas:
I spend a fair amount of time thinking about how things work or don’t, whether it be machinery or systems. 
A dozen Christmas songs I had not linked to yet this season. These are among my favorites.