All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Marriage is one of the great matters, as by marriage, a woman who was unlawful for a man becomes lawful for him. Hence, it is obligatory upon the one who is about to conclude a marriage contract to have full knowledge of it and thus he should not deputize someone who does not know its rulings. Whoever does not know should ask scholars pursuant to the Saying of Allaah The Almighty: {And We sent not before you except men to whom We revealed [Our message]. So ask the people of the message if you do not know.}[Quran 16:43]
As for the marriage mentioned in the question, it has defects in certain aspects, including:
Firstly, it is only done through writing. The marriage contract that is done through writing from the one who is able to execute it verbally is invalid according to the opinion of the majority of jurists of Maaliki, Shaafi‘i and Hanbali scholars, whether the two parties of the contract were present or absent. Hanafi scholars agreed to this (i.e. invalidating it) provided the two parties of the contract are present, and they allowed it if they (the two parties) are absent under certain conditions.
Indeed, we did not find any opinion for the Maaliki scholars that go against what they have mentioned here, not in Al-Mudawwanah nor in the commentaries on Khaleel. Let us state what the Maaliki scholars mentioned regarding this issue in particular. Ad-Dardeer said in his commentary on Mukhtasar Khaleel: "Gesturing or writing is not sufficient in concluding marriage except if there is a necessity because of dumbness."
He said in another place: "It (the marriage contract) should be entirely invalidated before and after consummating marriage, even if a long time has passed. The same ruling applies if one of the conditions related to the guardian, wife and husband or one of them is not met, or a pillar is not fulfilled, like if the woman gets married without the consent of her guardian or that the wording of marriage is not done verbally but through writing or gesturing or with a wording that is not legally accepted." [End quote]
The same thing was mentioned by the other scholars who wrote commentaries on Khaleel. Also, we have not found anything in Al-Mudawwanah that contradicts this opinion.
Secondly, the testimony of the guardian (on the marriage contract) is invalid because he is suspected of being biased. It was mentioned in Sharh Al-Kharshi ‘Ala Mukhtasar Khaleel Al-Maaliki: As for his saying, "Having witnesses other than the guardian in its (marriage) contact", he pointed out that the testimony of the guardian on the contract of the woman who is under his guardianship is not permissible, even along with others than him, because he may be suspected of concealing something (facts) about her." [End quote]
On the other hand, Shaykh Al-Islam Ibn Taymiyyah is of the view that the contract is valid if it is done according to all what people deem it marriage. He said in Al-Fataawa Al-Kubra: "Marriage is considered valid if it is done according to what people deem to be marriage through any language, wording or action." [End quote].
The majority of scholars hold a different opinion other than that as we have previously mentioned. Hence, such a marriage should be canceled and the contract should be renewed according to the proper way if there is a desire to continue marriage. However, the effects of the marriage remain effective such as attributing the child to the father and the like. For more benefit, kindly refer to Fatwa 92478.
Allaah Knows best.