en_tn/1sa/17/12.md

He had eight sons

Here the word "He" refers to Jesse.

Jesse was an old man...advanced in years among men

The two phrases mean basically the same thing and are combined for emphasis. (See: rc://en/ta/man/translate/figs-parallelism)

second to him Abinadab, and the third Shammah

This phrase shows birth order. AT: "Abinadab the second born, and Shammah the third born"