Is it permissible for my unmarried brother and me to share one Udhiyah sacrifice, knowing that our father does not pray and provides for us?

The Udhiyah (definition) (sacrifice) is a confirmed Sunnah (definition). One sheep is sufficient for a man and his household, even if their number is large. The household includes: the wife, children, and any relative who lives in the same house and shares the same living expenses with the head of the household. Therefore, if the questioner and his brother live with their father, and their expenses are shared, then one Udhiyah is sufficient for them, even if the father does not pray, because the Udhiyah is from the questioner and his brother, and not from the father.