Is the marriage contract considered valid under Islamic law, taking into account that one of the two notaries authenticating the contract did not physically attend the signing ceremony, but merely sufficed with their signature, despite both of them claiming witnessing with the phrase "We, the two notaries, bear witness..."? And does the presence of the notary and the groom's father as witnesses during the initial drafting of the contract rectify this flaw?

If your father and the one you named Al-Adl (the just one) were present at the time of the marriage contract and did not conduct the contract themselves, then their testimony is valid, and the problem is resolved.

If their testimony is not valid, then the Maliki school of thought does not stipulate the presence of witnesses at the time of the contract but rather considers it commendable. They deem it obligatory at the time of consummation. If witnessing occurred before consummation, then the marriage is valid. Signing or not signing the marriage document does not affect its validity.