Is it allowed for a woman to remove her Hijab in front of her stepfather? Also what is the opinion for someone who claims he is a Muslim, but does not pray? Please answer from the Qur'an or a Hadith of Prophet Muhammad (Sallallahu Alaihi wa Sallam).

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

As soon as a husband signs a marriage contract with a woman, the latter becomes Haram to his father.  Allah Says (interpretation of meaning) while naming the women to whom the man should not get married: {…the wives of your sons who (spring) from your own loins…}[4:23]. So, this one (the woman in question) is eternally forbidden for her father in law, whether she remains as a son’s wife or not.  Therefore, it is permissible for him to look at her to the extent that is permissible for him to look at his Maharim women.  As for the ruling of the person who abandons prayers read the Fatwa: 83025.

Allah knows best.