Is the marriage contract considered valid if one of the witnesses is the guardian's son and is 15 years old? And is the testimony of the guardian's son permissible in a marriage?

If a woman converts to Islam and has no Muslim guardian to marry her, and there is no Sharia (definition) judge in the country, then the guardianship of the Imam of the Islamic Center is valid. It is permissible for the acceptance to precede the offer, and the contract is valid thereby according to the three Imams, contrary to the Hanbalis. There is no specific age requirement for a witness; it suffices that he is a Muslim adult. The testimony of the Imam's son, who solemnized the marriage, is valid.