Is my friend's marriage legitimate, given that it was contracted with two women acting as agents on his behalf, in the presence of the girl's guardian and two male witnesses, along with public announcement? And if it is not, what is the solution?

A woman is not permitted to conduct a marriage contract (nikah) for herself or for another, whether she is a virgin or previously married. Her expression of consent is not considered valid in a marriage contract. If two women were to conduct the contract on behalf of or as agents for the guardian (wali), the marriage would be invalid according to the majority of jurists. However, if the guardian conducts the contract and the role of the two women is limited to merely documenting the contract (as registrars), then the marriage is valid.