The first families were the work T. L. Devinne was doing around 1899, details are on pages 47 and 48 of Southall’s Printer’s Type in the Twentieth Century. IIRC Stanley Morrison was also grouping existing types around the same time. ATF started using the term family in the early 1900s, the oldest specimen I have verified this in was the 1912 book.

Regarding Univers, what made the Univers package important was not what was offered, families like Cheltenham and Akzidenz were already doing that. What made Univers so special was that the whole family was planned from the start rather than releasing a few weights and later (inconsistently) designing more fonts based on demand from printers (although it did take several years for all of the fonts to hit the market, the release was not simultaneous). Univers was also released simultaneously for metal and photocomposition and available for license to anyone, another reason it was a big hit with designers. I think that Sebastian Carter wrote a detailed account in Twentieth-Century Type Designers, but my notes are missing so it might be elsewhere.

This from the Moore Type Foundry, Catalog No. 8, Toronto, 1929.

Here’s the Cheltenham family in use, 1905, one ad set in many styles.

Conceptually, Clarendon had always been used as a bold modern. This from the 1870s (note the “ack” - “ack” in particular):

Thanks for the scans Nick.
And thanks for the info James.

What about condensed fonts? The woodtypes of the 19th century are probably the earliest examples of typefaces with similar design