The bible and other texts use son of god, children of god and similar phrases metaphorically. It's strange why it should be taken literally.

The atheist Richard Dawkins engages in name-calling of the God of the Old Testament. "The God of the Old Testament is arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully." The atheist philosopher Michael Tooley cites Samuel 15:3: "Now go, attack the Amalekites and totally destroy all that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels and donkeys." Walter Sinnott-Armstrong in his book "Morality without God" cites Joshua 10:40: "So Joshua defeated the whole land ... he left none remaining, but utterly destroyed all that breathed, as the Lord God of Israel commanded him."

If the Pillars of Iman are belief in God, his angels, his books and his messengers and the day of judgement and fate, then this seems to be the case, no?

In reality, the New Testament consists of books by Jesus' followers.

Camilla Adang (1996) in "Muslim Writers on Judaism and the Hebrew Bible from Ibn Rabban to Ibn Hazm" cites examples of early scholars like Ibn al-Layth, Ibn Rabban, Ibn Qutayba, Al-Yaqubi, Al-Tabari, al-Baqillani, Al-Masudi and Al-Bukhari