Is my marriage religiously valid if my guardian is my irreligious brother, and my father is neither present nor aware of the marriage?

For a marriage to be valid, it must be contracted by the guardian (wali) or his agent, based on the Prophet’s saying, "There is no marriage except with a guardian." The woman's guardian is her father, then her paternal grandfather, then her son, then her brother, then their sons, then her paternal uncles, then their sons, then her father's paternal uncles, and then the ruler (Sultan).

If the closest guardian is absent in a way that would cause hardship and difficulty to reach him, the more distant guardian may marry her off.

If the closest guardian does not pray, he is considered a disbeliever according to the most preponderant opinion, and thus his guardianship is invalid.

If you asked the Imam of the mosque or the director of the Islamic center, and he issued a fatwa confirming the validity of your brother's guardianship, and he performed the marriage contract for you, then your marriage is valid, and you are not required to renew it.

If the ruler (judge) decrees the validity of a disputed invalid marriage, the marriage becomes valid and binding, and it cannot be annulled.