John Gill

Now there were seven brethren,.... In a certain family, at a certain place; perhaps at Jerusalem, who were brethren by the father's side; for such only were reckoned so, and such only did this law oblige: and the first took a wife, and dying left no seed: no child: hence it is clear that the ancient Jews used the word seed, of a single person, as these Sadducees did; though modern ones deny such an use of it in our present controversies with them about the sense of Gen 3:15; See Gill on Mat 22:25.