All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Firstly, it is not mentioned in the question whether this marriage took place with the permission of the guardian or not. According to most jurists, the guardian is a condition for the validity of the marriage, which is the view we prefer. If the marriage took place without the guardian’s permission, then it is invalid, unless it was held in imitation of the School of Abu Hanifah in not requiring a guardian. Besides, it should be noted that the Muslim ruler and whoever acts on his behalf can marry off the woman when she lacks a guardian, or that the latter is incapacitated, and so on.
Secondly, the marriage contract through modern means of communication is not permissible. Most of the contemporary scholars are of the opinion that it is invalid, and a decision in this regard was issued by the Islamic Fiqh Academy. However, some contemporary scholars are of the view that such a contract is valid.
Thirdly, it is required that both witnesses hear the offer and the acceptance. If one of the two witnesses hears the offer and the other hears the acceptance, the marriage is invalid. This is in addition to the fact that it is required for the two witnesses to know each individual among the spouses, and we do not know whether this has been verified or not. Our advice is to ask this question verbally to one of the scholars, so that he can clarify what needs clarification and issue Fatwa as the situation requires.
Allah knows best.