en_tn/rom/08/29.md

those whom he foreknew

"those whom he knew before he even created them"

he also predestined

"he also made it their destiny" or "he also planned in advance"

to be conformed to the image of his Son

God planned from before the beginning of creation to grow those who believe in Jesus, the Son of God, into persons who are like Jesus. You can translate this in an active form. AT: "that he would change them to be like his Son" (See: rc://en/ta/man/translate/figs-activepassive)

Son

This is an important title for Jesus, the Son of God. (See: rc://en/ta/man/translate/guidelines-sonofgodprinciples)

that he might be the firstborn

"so that his Son would be the firstborn"

among many brothers

Here "brothers" refers to all believers, both male and female. AT: "among many brothers and sisters who belong to the family of God" (See: rc://en/ta/man/translate/figs-explicit)