What is the ruling on money earned from photographing weddings where men intermingle with women who are immodestly dressed or unveiled, and the photographer uploads their pictures to his Facebook account?

It is not permissible to photograph weddings, and the money earned from it is unlawful and impure. The existence of a lawful job makes his money mixed. You must advise this person and remind him of the Sharia ruling. If he does not abandon his forbidden work, then it is not appropriate to accept marriage from him. And whoever gives up something for the sake of Allah, Allah will compensate him with something better.