What is the ruling on postponing the wedding after the husband swore "by that which is unlawful for me" that the wedding would not be postponed beyond its scheduled date, and would the oath by divorce be lifted before the scheduled date with expiation?

If the Islamic marriage contract has been concluded and only the wedding remains, then the husband's saying "She is unlawful to me" twice necessitates a single expiation for breaking an oath (kaffarat yamin). This is because the oath was repeated concerning the same matter before expiation was offered, and it can be offered either before or after the wedding. There is no need for divorce, as the oath is dissolved by breaking it, not by divorce. Once the oath is broken a single time, it is dissolved.