What is the origin of the use by Texans of "them" to mean one person?

Solution 1:

The construction that you describe sounds like an associative plural, rather than a use of the word "them" to mean one person. I'm basing this on the fact that if "them" meant one person here, "mom and them" would mean "mom and one other person," but it sounds like it actually means mom and one or more than one additional related people.

That is, it seems that despite containing the conjunction "and", the construction refers to a plural "them" that includes the named person.

Some languages have a dedicated construction for expressing this kind of idea; some languages apparently express it by just putting the word for "they/them" (without "and") after the person's name, as in Afrikaans Pa-hulle "Dad-them". ("Associative DPs", Hans den Besten, page 14)

Searching online for "and them" and "associative plural", I found the following sources that seem to discuss this construction:

• "Nouns & co. Converging evidence in the analysis of associative plurals", STUF - Language Typology and Universals 72 (4): 603-626, 2019, by Andrea Sansò and Caterina Mauri:

  in English we find the construction [X and them], which may be employed to convey an associative plural meaning. If we consider examples (13) and (14), we see no significant differences from examples (3)–(4): in both cases we can see a proper name followed by a 3rd person plural pronoun, the whole construction referring to a group composed by X and some further persons, to which X is associated by some context-specific relation.

  (13) Still, we have just been plugging away, and Max and them have all done really great and have worked so hard.
  (14) First Alex and them lied to us about the guns, and now they want to pretend like what happened didn’t happen.

  (page 13)

• The Electronic World Atlas of Varieties of English: Associative plural marked by postposed and them/them all/dem

• English . . . and Them! Form and Function in Comparative Perspective, Article in American Speech 75(4) · December 2000, by Sali Tagliamonte (I haven't been able to read this article)

This (along with similar constructions) is reported to be a feature of a wide range of English varieties, not just one particular area or dialect. E.g. "Appalachian English: morphology and syntax", by Michael B. Montgomery, 2008, has a section 10.5 "Associative plurals" that says

The phrases and all, and them (often reduced to an' 'em), and and those each mean "and the rest, and others" and are used usually after a singular noun to include associated people (especially family members) or things.

• [...]
• b. I have a picture of my dad and them working their own road.
• c. Helen and those were there.

The language Frisian, closely related to English, is said to have "Heit-en-hjar" literally "Dad-and-them" as a way to refer to Dad's family, Dad and mom, or Dad and one other person (den Besten page 16).