Is the marriage contract legally valid if it is conducted in the mosque in the presence of two witnesses for each of the spouses, and it is written by a female "marriage registrar" with full legal capacity?

For the validity of a marriage (nikah), the presence of a guardian (wali) and upright witnesses is required. If the guardian performs the marriage contract and two upright witnesses attest to it, then the marriage is valid. The woman's role being merely to write the contract does not harm its validity. Documentation is important for safeguarding rights, but it is not a condition for the contract's validity. If the woman herself acts as the guardian or one of the witnesses, the marriage is not valid, because a woman does not undertake the marriage contract (as a wali) nor can she be a witness to it, according to the preponderant opinion. However, if there were male witnesses other than her, then the marriage is valid, and her signing as a witness does not affect it. Supplication (du'a) is not a condition for the marriage contract.