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 is His slave and Messenger.
Any person who is present when the marriage contract is conducted is considered as a witness to it even if he is not appointed as a witness. However, it is permissible for the father of the bridegroom to be a witness according to the Shaafi’i School and according to a narration from Ahmad, but the testimony of the guardian of the bride is not valid. Khaleel Ibn Is'haaq, from the Maaliki school said (about the conditions of the marriage contract): “Having two trustworthy witnesses other than the guardian. Al-‘Adawi (from the Maaliki school) said: What is meant by the guardian is not the one who conducts the marriage contract but it is the one who marries off the woman.”
Besides, An-Nafraawi, from the Maaliki school said: “What is meant here is the one who has the absolute guardianship for marriage and not the one who conducts the marriage contract, and it is not a condition that the witnesses sign the contract; rather, their presence is enough.”
Allaah Knows best.