In him was life, and the life was the light of men
From the Haydock Bible Commentary
Ver. 4. In him: i.e. in this word, or Son of God, was life; because he gives life to every living creature. Or, as Maldonatus expounds it, because he is the author of grace, which is the spiritual life of our souls. — And the life was the light of men, whether we expound it of a rational soul and understanding, which he gives to all men; or of the spiritual life, and those lights of graces, which he gives to Christians. (Witham)
I would throw away the King James Version. It is not an approved Catholic edition. It is Protestant. The New American Bible is a terrible Catholic Edition. I suggest the Douay-Rheims. Reads like the King James Version, without any Protestant theology. In this case the KJV is more accurate than the NAB. Plus the NAB is using inclusive language ie. “human race”.
I would chose ‘in’. The greek in 1:4 is ‘en’ > ‘in’ , whereas ‘through’ is usually translated from greek-‘dia’. ‘dia’ translates mostly to ‘by’ & ‘through’ . Of the 2800 greek 'en’s in GNT 37 times or ~1.3% of the time it gets translated to ‘through’ in KJV , whereas 67% for ‘in’ like in DRB. I don’t know what stats are like in NAB…only have KJV on computer and GNT